Pondering a 3.5/D20 Modern Mash-up

[Lord Il Palazzo]

Like the title says, I'm thinking about running a game that mixes D&D 3.5 and d20 Modern and was wondering what advice the great and powerful internet might have. My basic plan is to start things out like the beginning of Men In Black; mundane PCs are going about their business (probably something police or military based) when things suddenly take a turn for the fantastic. After the mission's over, they are recruited into a secretive organization that monitors and polices paranormal beings that have come to earth from a parallel fantasy world. They end up based in a city that is the location of a lot of interplanar activity and will have (mostly episodic) adventures dealing with things that go bump in the night.

Starting out, adventures will mostly be local deals, as the PCs protect their assigned city but every so often I'll come up with an excuse for change of scenery and a maybe bit of globe trotting. At some later point in the game, an adventure will require the PCs to cross over into the fantasy world (which higher ups wouldn't allow before because the PCs were inexperienced and didn't have the clearance) broadening the scope of the campaign as we move toward the campaign's climax.

For characters, I'm thinking of starting the PCs at level 5 in strictly mundane D20 classes (no occultists, mages, etc.) Once they've signed on with the organization, they'll continue to gain levels but will have the option of training in D&D classes as well. I'm thinking ordinary level progression will be limited to d20 modern classes but that for ever 2 levels or so the PCs gain, they'll get to gain a gestalt level in a D&D base class. They'll only have basic training available from the organization so we won't go into prestige classes and such, just a reasonable selection of base classes (core and otherwise).

Enemies will come in a variety of flavors. Powers from the other side will try to establish footholds in our world. Monsters will prowl the dark corners of the city. Mundane villains will attempt to exploit creatures and artifacts from the other world.

Does anyone have any ideas or advice concerning such a campaign? Do my plans (particularly for character advancement) sound reasonable?

[shylocke]

It can work but some of the stuff doesn't quite crossover right. If you don't make the stuff from 3.5 have to deal with mass dmg, then the party is screwed. Also don't be a **** and use nuclear toxyderms. Those things are stupid OP

[shylocke]

Also look at the section 7( iirc) and shadowchasers campaigns in the d20 modern and urban arcana books. Pretty much what you are going for.

[Skysaber]

One of the things you'll be forced to do is mesh and integrate the skill systems. Trivial at first glance, but that's one of those projects that grows more complications the more you look at it.

Trust me, it's been a side project of mine for years.

[T.G. Oskar]

What you're explaining is basically Department 7 in a typical Urban Arcana campaign: mundanes breach the veil of Shadow, Dept. 7 recruits them, you start fighting against Shadowkind with spells and powers and magic items. The difference is that you're allowing D&D classes, which are arguably more powerful than d20 Modern classes, to an extent.

"To an extent" varies in terms of Tiers. Tier 1 classes (Wizard, Cleric, etc.) are powerful in D&D, and will be game-shattering in d20 Modern because the game was designed for a somewhat more gritty world. Any Wizard that exceeds 11th level will have more spells than the d20 Modern's Mage, though with a familiar of the same power and liberties on the feats provided (and no free Combat Casting). Same with Cleric and Acolyte, or Druid and Shaman (the latter from d20 Past), with the Cleric having better Turn Undead but the Acolyte having modern-world spells and some free feats, and the Druid keeping Wild Shape and a stronger Animal Companion (and more options, to boot). Tier 2 will be roughly the same as Tier 1: Sorcerers will be stronger than their d20 Past Sorcerer counterparts, though the latter also gets a lot of nifty goodies related to dragonkind. At Tier 3 (Bard, Psychic Warrior, etc.), things normalize a bit: the Battle Mind is like having 10 levels in Psychic Warrior and the remaining 10 in Soulknife, the Bard will be unique in what it offers (but it'll definitely like what a Charismatic Hero offers), and the Factotum might like to dip a bit in Shadow Slayer. By Tier 4, d20 Modern classes end up being better: the Ranger can barely compare to a Shadow Slayer (wins because of spells, but the Shadow Slayer gets a lot of goodies for combat specifically), the Barbarian and the Thrasher are almost identical... By Tier 5, d20 Modern classes are almost definitely better: a Strong Hero/Archaic Weaponsmaster or Strong Hero/Soldier can pretty much outpace a Fighter or Samurai, a Fast Hero/Swashbuckler (with maybe Musketeer from d20 Past with it) can match all but a Daring Outlaw Swashbuckler, and...the Paladin is hard to compare with the 5-level Holy Knight.

The reason I mention the differences based on Tiers is because that's probably what you'll meet when facing creatures from other dimensions within Earth; those are the classes that you'll meet. You'll rarely meet a Charioteer (to meet a Speed Demon in combat), and while the Wizard is pretty powerful, it rarely has the utility a Techno Mage might have (homunculus instead of familiar, able to cast spells through electronic devices and e-mails; maybe also through social networks :p), but a Bard will eclipse the ability of a Personality or Glamourist, a Psion will outmatch a Telepath...the list goes on. You'll have to make NPCs that are comparable, or you'll end up with creatures that simply can't compare. The fact that you're forcing them to have 5 levels in mundane classes and none of the FX-using advanced classes will put them at a disadvantage against pure classes, particularly if someone who was aiming for one of the FX classes suddenly meets Wizardry and the whole bunch of spells it gets compared to being a mere Mage. By the time your PC is a 1st level Mage (or Wizard), you can expect a 4th level Wizard with 2nd level spells but none of your talents...of which only a few might work (Plan is pretty cool, and Exploit Weakness means your rays will hit better than the Wizard's ones because you're using Int for attack rolls). Aside from the class bonus to Defense, you'll end up with shifts in balance that will be so violent, it'll definitely hinder the game.

My recommendation is one of two: either define which class system you'll use, and then keep to it (what d20 Modern uses: a 6th level Wizard might be a 3rd level Smart Hero/3rd level Mage in this world, and probably recalls some of its old spells but never gets to its old level of power), or go gestalt. Gestalt will be a bit more complex: basically, you have to force one side to remain d20 Modern, while the other can go into D&D. That means you can have, for example, a Paladin 5 on one side and a Dedicated Hero 3/Acolyte on another, thus allowing a Paladin with two sides of spells but better BAB. The Gestalt approach allows you to have characters that are undoubtedly special, allows them to safely handle most D&D creatures in this world, but it'll have a degree of power slightly higher than the norm; it's not the same to have a Wizard 5 than to have a Wizard 5 with a side of Fast Hero 3/Gunslinger 2, probably keeping as a Wizard in one side and aiming for, say, Spellslinger (one of the PrCs from the Urban Arcana web enhancement) on the other side, because you'll be capable of using the Wizard's spells for the Spellslinger's talents, and couple your unbeatable spellcasting with high AC/Defense and the use of firearms. Your BBEGs could also have this "benefit", making them real menaces to your characters.

Once you handle the class into something "balanced", the rest isn't that hard. You'll have to make some equivalences (AC and Defense are the same thing, Treat Injury is better than Heal, some knowledges like Arcane Lore and Theology & Philosophy are similar to Arcana and Religion), but otherwise the game is pretty similar. It's on the class system where you have to be the most careful, because the power levels in d20 Modern and D&D are VERY different.

Also, not just nuclear toxyderms: I think, by theorycraft, a 4-member party of d20 Modern characters can't beat a Dragon of the same CR, not even early on. Things get worse when they use magic.

[Lord Il Palazzo]

I did notice the Shadow Chasers and Urban Arcana campaign settings (I've actually spent a good chunk of the last few nights reading them) but what I'm looking to do is somewhat different from both. One of the big problems I have with both is that creatures from the other side (the Shadow, as the official sources call it) have no memory of their previous lives. I'm hoping to run something with cross-planar conspiracies and at least the potential for some level of cooperation between different factions in different worlds, so that wouldn't fit well. I'm also looking to run a world where magic originates entirely from the other world so having a lot of Urban Arcana's techno-magic and modern magic items wouldn't make much sense. That sort of thing might develop as the setting ages (I could definitely see a player character researching spells that fit into a modern setting as he gets learns more about what magic can offer) but I don't want it hardwired into the game.

I get that different tiers have different power levels relative to D20 modern material, but I've never been one to restrict my players' options based on power-level concerns. Part of the reason I'm looking at the gestalt approach I described is that it gives the D20 Modern material room to shine by giving the players more levels of it while also keeping the D&D material from getting to the point where players who pick pure caster levels completely overpower more physical characters.

Department 7's been a little bit annoying, actually. It's identified as an organization that fights shadow creatures but there's virtually no specific information on it in the D20 Modern Core Rule Book besides a bunch of suggestions for different campaign models (make it a government agency, make it a private institution, etc.) Maybe the Urban Arcana book's got more concrete and useful stuff (I haven't gotten in too deep to that one yet) but as it is, it looks like I'm going to have to do a lot of the creative heavy lifting on it myself anyways so I'm not really sure what good the few details in the book really are.

Skysaber: I don't suppose you've got any suggestions or tips on integrating the skill systems. It doesn't look too tough at first glance so if nothing else I'm curious what sorts of complications you've run into.

[PraxisVetli]

(Anti) Paladins need to be able to summon mounts cars.
I picture the classic Blackguard calling forth his ride, the sky turning red and maelstromy, and a lightning bolt smashes into the ground and when it clears, there she is.
"In the name of Rage and Horsepower, I call upon the mighty FERRARI!!"

[T.G. Oskar]

(Anti) Paladins need to be able to summon mounts cars.
I picture the classic Blackguard calling forth his ride, the sky turning red and maelstromy, and a lightning bolt smashes into the ground and when it clears, there she is.
"In the name of Rage and Horsepower, I call upon the mighty FERRARI!!"

Bah. Summoning fiendish Ferraris are overrated. Maybe if it was a Lamborghini Diablo (since it fits), but...

Choppers. No self-respecting Blackguard would leave the chance to summon a chopper with black fire design, fuming the most hideous smoke around, and with a MPS of 1000 miles to a soul (hey, maybe that Blackguard is eco-friendly!). Paladins might instead summon police motorcycles, or perhaps chromed Harleys, with the exhaust pipes looking like wings.


I did notice the Shadow Chasers and Urban Arcana campaign settings (I've actually spent a good chunk of the last few nights reading them) but what I'm looking to do is somewhat different from both. One of the big problems I have with both is that creatures from the other side (the Shadow, as the official sources call it) have no memory of their previous lives. I'm hoping to run something with cross-planar conspiracies and at least the potential for some level of cooperation between different factions in different worlds, so that wouldn't fit well. I'm also looking to run a world where magic originates entirely from the other world so having a lot of Urban Arcana's techno-magic and modern magic items wouldn't make much sense. That sort of thing might develop as the setting ages (I could definitely see a player character researching spells that fit into a modern setting as he gets learns more about what magic can offer) but I don't want it hardwired into the game.

I get that different tiers have different power levels relative to D20 modern material, but I've never been one to restrict my players' options based on power-level concerns. Part of the reason I'm looking at the gestalt approach I described is that it gives the D20 Modern material room to shine by giving the players more levels of it while also keeping the D&D material from getting to the point where players who pick pure caster levels completely overpower more physical characters.

Department 7's been a little bit annoying, actually. It's identified as an organization that fights shadow creatures but there's virtually no specific information on it in the D20 Modern Core Rule Book besides a bunch of suggestions for different campaign models (make it a government agency, make it a private institution, etc.) Maybe the Urban Arcana book's got more concrete and useful stuff (I haven't gotten in too deep to that one yet) but as it is, it looks like I'm going to have to do a lot of the creative heavy lifting on it myself anyways so I'm not really sure what good the few details in the book really are.

Dark*Matter has a nice definition of Department 7, as part of a NGO called the Hoffmann Institute. There's 12-13 departments, and Department 7 is the one that deals with paranormal investigation. The others are research departments, PR, and so forth. Thing is, Department 7 is left bare so that you can define its purpose. One might define Department 7 as an actual government organization (like the Dept. of Homeland Supernatural Security from the webcomic Use Sword on Monster), a secret conspiracy who happens to be the nicest one, the supernatural division of MiB (remember that, in the original comics, the Men in Black also dealt with supernatural entities; while Division 6 in NYC deals with aliens, Division 7 on...somewhere else deals with the Shadow Creatures), or...really, whatever you like. There's some documents around that can help, including a field manual for Dept. 7 agents, detailing the procedures they should follow (such as how to ID tracks, the procedure to confirm a Shadow case, and even what happens if you run afoul of the Shadows), if you need some more info.

One thing I might want to mention is that, if using a Gestalt approach, or even your original approach, some d20 Modern/Urban Arcana feats (mostly the Urban Arcana feats) won't play nice. By no means allow a class that grants quickened progression (Ur-Priest, Sublime Chord, Nar Demonbinder; Divine Champion is fair play though) access to the Ecclesiarch or Urban Arcana's Archmage class, unless you want more 9th level spells than a Cleric would ever dream of (and the ability to progress your CL to your character level); Ur-Priests might also get the odd ability to rebuke up to their character level if they step on Ecclesiarch, so... Fortunately for Clerics or Wizards, while you get double spells, you only get up to 7th level spells if you wish to get to those before 20th level, as they're basically like the Hierophant in terms of progression. It goes without mentioning that you should NEVER, by ANY circumstances, attempt to allow a full-class Wizard or someone with full spellcasting to access Ecclesiarch while going Gestalt, because the exact wording is quite friendly (20th level Wizard with CL equal to its character level plus any other bonuses, and then you get 8 spells per spell level on top of that).

On the other hand, Battle Mind and Martial Artist are VERY friendly on a Gestalt progression. A Monk might consider, since it already counts as having Combat Martial Arts (it's mostly like Improved Unarmed Strike), to get the Improved and Advanced Combat Martial Arts feats, so they get a nifty weapon (19-20/x3 unarmed strke). Defensive Martial Arts is nice, but the abilities it offers are just as good; Combat Throw adds another +2 to grapple and trip checks (and requires no Int), and Improved Combat Throw allows tripping if someone fails a melee attack against you (no need for Robilar's Gambit or Karmic Strike, and it's accessible MUCH earlier). You'll have to consider how feats work, mostly, since there's a few feats that are great for melees, and if you're Gestalting, be pretty sure that the characters will end up with an assortment of extra feats which can be pretty decent.

Have you considered stuff from d20 Past, d20 Future, d20 Apocalypse, Dark*Matter or d20 CyberRave (basically, the other sourcebooks)? I mentioned a few of the PrCs from d20 Past, but not all: the Scientist is the pulp fiction's response to the Artificer (note: don't let them mix, it's a bad idea), the Gangster is much like the Rogue... d20 Future has, of course, classes that are for future missions, but you can easily port the Field Officer if you'd like (surprisingly great buffer, specially if coupled with the Marshal and having Charismatic Hero levels on top); not sure about the Dreadnaught, though. d20 Apocalypse deals with end-of-world situations, but it has lots of new outsiders to play with, including Angels that are closer to typical Earth mythos than D&D versions. Dark*Matter not only explains the Hoffmann Institute, but also has new spells for Mages and Acolytes, new powers for Battle Minds and Telepaths (which you may consider for purposes of "Earth-based magic", specifically the ones related to the Loas), and a few...interesting PrCs (the Alchemist not so much, but definitely the Diabolist and the Visionary).

BTW: your stance on aliens? The only thing I'd differ with from most people trying to mash D&D and d20 Modern is that I'd definitely allow one or two aliens (though I'd be VERY careful of allowing the Fraal access to magic or psionics; those little guys are the ultimate race for most magic or psionics).

[Lord Il Palazzo]

I absolutely see what they were trying to do with leaving Department 7 open to GM interpretation, it's just that it bugs me. In a game where practically everything's already open to GM interpretation anyways, leaving a major detail a complete blank slate isn't exactly helpful. I prefer when publishers take the time to say "here's what we envision; adjust as you see fit" rather than just saying "here's an empty void; make up whatever you want in it". Having that starting point is a big help when you've got a whole world you're trying to build and populate.

I haven't actually given much thought other books; I've pretty much got my hands full with the D20 Modern Core Rulebook and Urban Arcana right now. I'm not planning bring in any futuristic or sci-fi elements so I imagine the future books is a bit outside the scope of what I'm looking for. (Aliens are out too, for the same reason. I'm keeping the setting realistic except for the encroaching magical world. I don't want to get things too complicated for our first outing with D20 modern.) From what I've heard, D20 Past might be handy.

Like I said in my first post, I'm planning to keep the D&D classes pretty minimal compared to the Modern levels, maybe allowing one D&D level in gestalt with every 2nd or 3rd D20 Modern level and to only allow a base classes (after all, the department can't have trainers on hand for every possible prestige class). That way, even if the game went as far as level 15 (which I'm not sure I expect, though it would be possible, I suppose) we still wouldn't have more than 4th or 5th level spells floating around. I'm honestly not sure what to do with the magic based classes in D20 Modern/Urban Arcana, but I'm thinking that if I'm allowing magic in via D&D classes, I might keep the D20 modern stuff to the mundane classes. If all magic comes from the other world, it wouldn't make sense for any that's specific to our world to be floating around.

In the end, I may keep both options on the table and give the players the choice of how they want to handle things when the time comes. I could explain the two leveling systems I'm thinking of (strictly D20 Modern, with Urban Arcana vs. D20 Modern base with D&D gestalt) and see what they think would be more fun.

[T.G. Oskar]

If it helps:

Since you're eager to limit the impact of base classes, you're better if you do as follows:

The Mage and Acolyte already bring up to 5th level spellcasting, much like the Cleric and the Wizard, so they could effectively replace your Mage and Acolyte advanced classes. Have the Wizard/Cleric (for Earthlings) require the same as a Mage/Acolyte, and make the Wizard and Cleric Advanced Classes. No matter what, limit their progression to 10th level; that way, you can only access up to 5th level spells, and get mostly two or three feats. The Wizard might replace Scribe Scroll with, say, Scribe Tattoo or Brew Potion at 1st level, and get three feats at 3rd, 6th and 9th (as the Mage), adding all metamagic feats, item creation feats and the unique list of the Mage. If you want, a 10th level Wizard in your campaign automatically gets Spell Mastery for free, as a kind of "capstone". The Cleric, on the other hand, gets tacked on the prerequisites of an Acolyte, and bonus feats on 3rd, 6th and 9th, allowing access to all Acolyte bonus feats; they also keep their domains. The new Cleric MUST follow either a deity or one of the four alignments (Chaos, Evil, Law, Good) as their allegiance. You're on your own to add the ability to turn or rebuke Magical Beasts and Outsiders, but likewise limit Clerics to 10th level.

Fighters are pretty similar to Archaic Weaponsmasters (from Urban Arcana) or Soldiers, so your best bet is to have the Fighter merge somewhat with both classes. You can be a Soldier with extra feats (of the Fighter bonus feat list) and its own (most likely the firearm feats), or an Archaic Weaponmaster with extra feats (of the Fighter bonus feat list). Shadowkind can only be Archaic Weaponsmasters; Earthlings can usually be Soldiers, but once they tap into the Shadow, they can also become Archaic Weaponmasters. Important, though, is that BOTH must have full BAB. Have the bonus feats for Soldiers appear at the levels a Fighter would otherwise get them (1st, then every even level), and move class features up or down to cover up for dead levels.

Barbarians and Thrashers are essentially the same, but I'd keep them distinct. You can't be both a Barbarian and a Thrasher; Shadowkind are usually Barbarians, while Earthlings are usually Thrashers. Treat the Barbarian/Thrasher bit as per the ability of Blackguards to trade Paladin levels for Blackguard levels, but instead, you trade Barbarian levels for Thrasher levels, and no turning back. You *might* justify an Earthling taking levels in Barbarian if they have the Primitive occupation, though.

Martial Artists are Monks without their supernatural abilities, so I'd feel VERY tempted to make Monks a Prestige Class, which you can only access if you have levels in Martial Artist (you can say that a character needs the Living Weapon and Iron Fist class features). Most people say that Monks are mostly a 2-level class, so try to cram as many class features as you can into a Monk PrC of 5 levels; 1st level could have Stunning Fist for free with the Monk's special caveat, 2nd level could have Wholeness of Body, 3rd level could have Abundant Step (usable with an action point!), 4th level could have Spell Resistance and 5th level could have Quivering Palm. Between a Martial Artist Advanced Class and a Monk PrC, you can make a slightly better Monk than before. Make sure that the Monk progresses Living Weapon, and maybe add the ability to apply your Wisdom modifier to your AC if unarmored. Perhaps even Slow Fall and whatnot.

Rogue...Rogue's a bit difficult. I mean, it's basically 10 levels that grant 5d6 Sneak Attack, Evasion, Uncanny Dodge, Trapfinding and special abilities. You could make the Rogue an Advanced Class that requires the Evasion and Uncanny Dodge 1 talents of the Fast Hero, grants Sneak Attack every odd level, and spread the remaining class features between the other levels (bonus feats at levels 3, 6 and 9 as usual; Special Abilities at 4th, 8th and 10th levels; remove Defensive Roll and Opportunist as they're Fast Hero talents). They still keep their huge skill list, but Earthling Rogues gain no access to UMD (unless you allow them to; then again, Earthlings can get the skill through Arcane Skills).

Paladins and Blackguards are far better than the Holy/Unholy Knight, so try to take a cue from the Holy/Unholy Knight PrC, the Prestige Paladin PrC and the Blackguard PrC, and make them a 10-level Advanced Class. You might also want to consider Lawful and Chaotic variants (Anarch and Justiciar?). A Paladin must uphold an allegiance to Good, and get certain skills as prerequisites (the Prestige Paladin requirements of Knowledge [religion/theology and philosophy] is decent; perhaps Knowledge [nobility and royalty] for Shadowkind or Knowledge [civics?] for Earthlings, and definitely Diplomacy); the Blackguard gets perhaps Intimidate and Knowledge (religion/theology and philosophy and an allegiance to Evil, while a Justiciar MUST have Knowledge (civics) and an adherence to Law. From there, base off the Blackguard as a PrC and build the Advanced Classes from that: they get up to 4th level spells (or maybe 3rd level?), no bonus feats from high ability scores (the same penalty as Holy/Unholy Knights, so they get very little spells), bonus feats (as all advanced classes), and similar class features, with something that allows each Advanced Class to distinguish beyond the aura of Courage/Despair/Resolve/whatever you add to Justiciar. You might also impose the requirement of some sort of contact with an exemplar of the allegiance (not necessarily an outsider, but perhaps being ordained by a Bishop, a bonafide outsider, or perhaps a magic item that embodies the allegiance).

The d20 Past Sorcerer is better than its D&D counterpart, so I'd say ditch the D&D Sorcerer; you might want to play with the class features to awaken the other heritages of the Sorcerer (Celestial, Infernal, Fiendish, Fey), and allow Heritage and Draconic feats as bonus feats. The Druid is on an odd standby, since the Shaman is basically the same but has the ability to meld with its Animal Companion instead of Wild Shape; I'd really consider the Druid playing much like the Shaman, ditching Wild Shape altogether; the Druid wants it, he (or she) should become a Shapeshifter (the PrC from the Urban Arcana Web Enhancement). The spell list of the new Druid/Shaman should be a blend of the Druid's and the Shaman's own.

That leaves the Bard and the Ranger, which are the only classes that are the most difficult to replace in a d20 Modern Setting. Fortunately, they have Prestige progressions, so you could use that as a basis to make their Advanced Classes. IMO, Bards could have the prereqs from their Prestigious counterpart, but replace the spellcasting requirement for a talent requirement from the Charismatic Hero. Inspiration is already the same as Inspire Courage though slightly better, so I'd consider that as the requirement. The other songs of the Bard could be used through action points instead of Bardic Music, and spread nicely through 10 levels. This leaves Bards with 4th level spells, though, so you might want to consider tweaking their spell progression a bit.

The Ranger is the hardest class to work with, though. Definitely, you'll need to reduce the BAB requirement of its prestigious counterpart to +2, so medium BAB classes can enter. Knowledge (nature) is hard to nail in; the closest is Knowledge (earth and life sciences), so you might need to work with that one. I'd also add, just because, Knowledge (tactics); the Ranger must know about various combat tactics. You may choose to waive the feat requirement, and you should definitely dump the spellcasting requirement. This makes the Ranger's fastest entry a Dedicated Hero, and with the Empathy and Healing talent trees, it's pretty good; on the other hand, you'd expect a Ranger to enter from Fast Hero, which also has nice stuff for them, but nothing really aids you to enter as a Fast Hero unless you have the right occupation (they don't even have Knowledge [tactics]!). No matter how you work that out, the Ranger should progress its spellcasting much as a Blackguard would, and progress its animal companion as would a Wildlord. The bonus feats of the Ranger would be geared towards combat styles. You could make the feat requirement focus on a specific combat style, choosing from Two-Weapon Fighting, Archery, Marksmanship (starting with Personal Firearms Proficiency, going into Advanced Firearms Proficiency and ending on Burst Fire and maybe Strafe) and perhaps one or two others. Try to make it so that a Ranger could easily get into the SpecOps Prestige Class; that'd be fun.

That covers the base classes, and even one prestige class (the Blackguard). You can probably cover up the PrCs likewise: Arcane Archer and Spellslinger are pretty similar, but in the same way a Barbarian and a Thrasher are similar; Archmage and Hierophant are basically the old-school equivalents of Urban Arcana's Archmage and Ecclesiarch, so try to keep them separate (and maybe rename one of them). Horizon Walker could easily be an Advanced Class exclusive to Shadowkind, which could then be later applied for your characters as they advance; they'd get less Terrain Masteries and perhaps no Planar Terrain Masteries (or get them very late), and get a few bonus feats and maybe some other class features instead. The Swashbuckler does most of what the Duelist does but better, and also makes a perfect replacement for Complete Warrior's Swashbuckler class, so might as well take what the Swashbuckler lacks and spread it between that class and d20 Past's Musketeer. The Assassin could be a 5-level PrC that lacks spells (I can't believe I'm saying this, but perhaps the PF version of the Assassin might work better for this kind of thing), but gets Death Attack and some other goodies (and maybe full BAB!). Eldritch Knight... is iffy. I'd probably go with Spellsword instead if you want to combine spells with swords, but provide no progression to spells (except for maybe caster level) and some sort of channel spell ability (much like the Spellslinger's Spell Bullet). The Mystic Theurge is definitely a worrisome PrC, since it requires you to learn Cleric and Wizard (or, really, Arcane and Divine) spells to work; consider at your own risk. Dwarven Defender would make for a pretty nice Tough Hero Advanced Class, maybe if stripped of its racial requirement. Loremaster...not sure about that one; Shadowdancer is really difficult to adjudicate. Thaumaturgist works well as a 5-level PrC of its own, and you could make it capable of existing without spellcasting ability whatsoever (maybe capable of learning incantations that mimic Planar Binding or Planar Ally).

As for the magical progressions of d20 Modern and Urban Arcana...I mentioned about Mage and Acolyte already, so let's go with Mystic and Techno Mage. The two could exist nicely, though Mystic and Favored Soul have a slight conflict between each other. Before the incursions of D&D characters, you could allow Occultists (and maybe Spiritualists) to exist as they usually do, since they're meant for low-magic campaigns. In the case of the Techno Mage, they'd be VERY late developments, most likely after 10-20 years of incursions where Wizards manage to use the Internet favorably, so it's your decision if they're available or not. The other classes, save for the ones I mentioned and Psionic Agent, are fair game: the Shadowjack is tame enough to use before incursions, though you must be careful to deal with the Online Spell Resistance Shadowjack ability and their capstone, Virtual Incantations (depending on how "supernatural' you want your Shadowjacks to be). Shadow Hunter is sorta similar to Ranger but without spells and animal companions, so it's your choice if you want to keep it or merge it into Ranger.

Now, as for the other base classes in other D&D supplements: the Swashbuckler has already been dealt with, as the Urban Arcana Swashbuckler is pretty good as a replacement (you might want to add some of the Complete Warrior's Swashbuckler's abilities to the Urban Arcana ones, particularly Insightful Strike and maybe the abilities that rely on Critical Hits instead of Weapon Focus/Weapon Spec.). The easiest to deal with would be Ninja (much like the Rogue; it could be a PrC that can be accessible from the Rogue or Martial Artist advanced classes, tho) and Scout (work it around, and you have yourself a nice advanced class; think of its effect with guns!). Samurai is actually a build, and Archaic Weaponmaster works wonders to replace it, so ditch Samurai. Warlock is phenomenal (particularly with Diabolist), so consider how to port it as well, if you want to; again, 10-level advanced class, probably up to Greater Invocations. Hexblades and Duskblades could enter (and with Duskblade, you solve the Eldritch Knight predicament), but they're pretty hard to pass through; likewise with Shugenja, Spirit Shaman, Favored Soul, Warmage and Beguiler, and so forth. As I mentioned on my second post, the Artificer and the Scientist are an interesting comparsion; the Artificer creates magic items and has infusions that temporarily enchant items to duplicate spells, whereas the Scientist creates contraptions that act as spells (a reason why I say the two don't mix well); you're on your own to determine if they can pass, though the Artificer would be wisely limited to 10 class levels, maybe 4th level infusions and would require changing the Artificer PrC's name to something else. Oh, and...Marshal/Field Officer. They're so pretty together...

This, IMO, works better than attempting a hindered Gestalt as you propose; my idea was to go full Gestalt, but treat your players as special snowflakes, dealing with creatures potentially more powerful than they are. Stunted Gestalt will be really weird, makes for an awful progression, and is less elegant than merging the two class systems into one, even if it seems simpler in paper.

As for Shadowkind? Well, they're cheaters; they start off exactly as a D&D character would. To keep it fair, they can't multiclass into Earth classes (so your characters could end up as Fast Hero 5/Rogue 10, but a Shadowkind character couldn't get into Rogue 10/Gangster 10 or something like that), and they're also limited to 10 levels in base classes. You'll also have to work in Defense bonuses to AC; they won't get Reputation bonuses, as they'd be unknown, unless they have the Renown feat or do acts that grant them reputation bonuses.

Not sure if I forget anything, but...maybe not add Healer into the game? A Dedicated 3/Field Medic 7/Cleric 10 could do better than a Healer would ever do, save for its Celestial companion, since you'd get better spells, Heal/Treat Injury works better in d20 Modern, and you don't really need all those SLAs, plus a 7th level Field Medic can revive people without the need of magic, so that's one where it simply outclasses the Healer, hands down.