Have you ever used different systems for different components of a game?

[Coidzor]

Like, say, used Call of Cthulhu's skill system with a few tweaks to the setting for the purposes of exploration, investigation, and social interaction, but used something like D&D for combat scenarios?

Or used one system for when characters were outside of their mecha and then switched over to another system for vehicle/mecha sections?

[Knaight]

While I haven't done this, I have used base systems that are very flexible and easy to do house rules in, and done extensive modifications involving pulling things from other systems.

[Madeiner]

I ended up not doing it, but i wanted to incorporate Dread's JENGA rules instead of stealth rolls in d&d, for infiltration missions. It looked perfect in theory, but i never got to try it.

[hifidelity2]

I have used different system but normally for large battles (where players were generals / elite unit) but wanted to play out the whole battle
so
Mixed AD&D and Reaper
Mixed SpaceMaster and Full Thrust

[Ogh_the_Second]

Indeed, for large battles.

Also, I have regularly used refluffed board games & card games to e.g. put players in the shoes of different factions' leaders, and then using the results of those conflicts as the backdrop for the DnD story.
Just last week, I have converted a Formula-D track to depict a camel race taking place in the DnD adventure. Before, we have done a similar thing with the Viper game to emulate other 'run the gauntlet'-like situations.

[sktarq]

I've played in such a game but not run one.

Used the Warhammer40K rules for small parties as the combat system (mostly). . . used Rifts/Palladium for non combat systems. . . it kinda worked but how much of that was just because a group of experienced players just rolled with it. If new people, rules lawyers types, or argumentative people were involved then I don't know if it would hold up.

Edit setting was some homebrew of based, at least in part, on the wormwood splat for RIFTs if it had a couple crashed orbital cities growing out of it.

[Xuc Xac]

I played Rifts once. That had a different system for everything.

Old D&D too. Sometimes you want to roll high, sometimes low. Sometimes you roll 1d20, sometimes you roll 2d10 (or 1d12+1d8 for some reason), sometimes you roll d%. Some characters cause surprise on a 1, 2, or 3 on a d8, some only get surprised on a 5 or 6 on a d6, and nobody knows what happens if they meet.

[NichG]

I had a campaign with a homebrew application of 7th Sea rules to a very different setting. The power level in the game was getting pretty high, and making interesting opponents within the 7th Sea framework became sort of difficult. So I tried something crazy and was shocked how well it worked: I just switched to D&D rules for enemies (big boss monsters and things like that, primarily). The number of flesh wounds dealt converted straight to hitpoint damage, and 7th Sea roll-and-keep attacks were used as is against AC. The 7th Sea characters will be better at dropping special effects on enemies than D&D characters would be at high level (because of the way saving throws vs saving throw DCs scale in high-end D&D), so it keeps that aspect of the game relevant for longer, but at the same time 7th Sea-type characters tend not to have save-or-die/save-or-lose abilities.

A couple opposed roll situations can get mathematically wonky, but it required surprisingly little adjustment overall.

I also played in a game that had a mashup of L5R and World of Darkness rules, which was weird in places but didn't seem too bad. The game didn't get very far so we didn't get to really put the mashup through its paces - I had the feeling that combat was going to be excessively lethal, even more-so than in standard WoD, because L5R has a nasty death spiral component which is normally somewhat balanced by being able to become a defensive bulwark, but in WoD you often need to sacrifice your next action to actually defend against an attack. So the combination means that multiple opponents is really brutal, and even against a single opponent its a bit like playing rocket tag out the gate. So, seeing that, we avoided combat like the plague, and as a result didn't actually test it out.

[wumpus]

A friend of mine had the Stormbringer game as was told that it played better using the full Runequest rules for combat (it used some sort of Runequest-lite rules instead). Looking at Runequest's wiki page, it mentions Stormbringer as a derived game. I've heard of playing Gamma World (the earliest edition, although I doubt the genre was popular enough for another after the cold war ended) with AD&D rules (mostly where Gamma Rules simply didn't cover much).

Hint: If you are playing a game derived from a more "well covered" game, I highly recommend picking up the "well covered" game and scrounging it for rules.

Both of these involved playing with games clearly derived from a "flagship" game. Using others would be difficult, although it might work for anything largely inspired by other games. My guess is that such games would either be very close (having the right character attributes to base the rules off of) or very far. such that the rules don't interfere too much. I'd guess using some Exalted rules in the above games might work, assuming that they are different enough not to interfere.

Trying to work Traveler rules (where everything is 2d6) into a d20 game would mean breaking out the probability textbooks and deeply re-working the rules to try to match the underlying chances. I can't imagine it would be worth my time.

[Quertus]

I played in a homebrew that used, IIRC, call of cthulhu for skills, Calvin ball for magic, and D&D for combat.

I've long thought it would be cool to play a magic cyber space game. My dream mash up so far would use D&D for race, shadowrun for cybernetics, WoD Mage for magic, heroes for initiative, warhammer fantasy for mutations... WoD for XP, Shadowrun for rerolls... maybe a cross between shadowrun and mutants & masterminds for character creation, with flaws from WoD. But no one system has really caught my eye for ships, space travel, ship combat (Babylon 5 a call to arms?), "normal" combat, or skill use. And no one I play with knows all these systems.

[goto124]

Trying to work Traveler rules (where everything is 2d6) into a d20 game would mean breaking out the probability textbooks and deeply re-working the rules to try to match the underlying chances. I can't imagine it would be worth my time.

Unless you use online dice rollers to do the d20s and 2d6s. But that's probably heresy for not using physical dice.

Calvin ball for magic

Is Calvin ball an actual system, or did you mean "freeform"?

[Hyooz]

I had a short-lived Decking-focused Shadowrun game that used those mechanics for most things, but once you were on the net, we switched to a variant of 4e's combat rules because it was secretly a Mega Man Battle Network game.

[wumpus]

Unless you use online dice rollers to do the d20s and 2d6s. But that's probably heresy for not using physical dice.

The problem would be more like "opposed rolls" where one is a rolling a 2d6 (or at least with 2d6 bonuses) and the other is rolling with a d20 (with similar bonuses). Which is more effective: a +3 fantasy crossbow and a +4 BAB, or 3 ranks of marksmanship and a carbon-fiber crossbow* (which might not give +2 in a 2d6 system).

* Note: when I was a boy scout I learned that pretty much any rifle was legal [unregistered] where I live, but crossbows needed to be registered (and only handicapped people cant hunt with them). Something about silent, [soft] armor penetrating, and zero muzzle flash makes people (and moreso cops) antsy.

[Quertus]

Is Calvin ball an actual system, or did you mean "freeform"?

I mean freeform. Magic In that game literally consisted of two three things: a magic stat, a mana pool, and a descriptor (which was usually "magic"). After playing that system with that GM, I have to say, he's one of the few people I feel comfortable with making stuff up on the fly. You want to do what? Teleport away, but leave an illusion of yourself behind? Transform that guy you just killed's corpse into a copy of yourself? Swap the entry and exit wounds? Condition someone to feel happy every time they see you? Steal people's bad luck, and use it to perform mercy killings on the terminally ill? Absorb people's memories and skills? Yeah, you can try - here's the (to use modern terms) DC, and here's the cost.

[Nero24200]

I've thought about running a hack//sign style campaign were the party try to track down a murderer, with their RL investigation stuff using something like M&M and 4th Edition D&D for the game world.

Though I encountered 2 problems with this...
1. My group probably would never touch 4th Edition with a ten-foot pole, and we had a recent M&M campaign that ended badly due to some of the mechanics not meshing well with my group.
2. I worried the "RL" element may have too strong of an influence. For instance, a player losing access to their IG computer would effectively lock them out of entire sections of the campaign (even if only temporarily). I'm still trying to think of ways to balance it.

[2D8HP]

First RPG played was oD&D mixed with then incomplete 1e AD&D. Later mixed in Runequest/Stormbringer/Call of Cthullu, magazine suggestions, winging it etc. I now wish we weren't such snobs and had tried mixing inTunnels and Trolls as well. We did snobbishly however briefly, and unsuccessfully try mixing in Chivalry and Sorcery. One of the best DM/GM/referee/Keeper in our circle had us try Rolemaster/MERP of which I can remember little. We also played other genre RPG's (Traveller, Villians and Vigilantes etc) and alot of Car Wars which we turned into a RPG. There is much that I miss about those times (cue Auld Lang Syne).
Now you kids get off my lawn!

[Thrudd]

This trend actually goes all the way back to the beginning. Original D&D was designed for dungeon delving "heroes". Chainmail rules would take over for the mass battles, which were an expected part of the game, and the board game Outdoor Survival by Avalon Hill was used for wilderness travel.

Battlesystem was created in the mid eighties as a new large-scale battle game intended to dovetail with AD&D, this is another similar example.

Mechwarrior RPG and Battletech is another example. I assume the designers intended for them to dovetail together, that is how we played it, using Mechwarrior RPG to roleplay scenarios of our pilots in between big mech battles. The Battletech battles were really the best part and what we spent the most time on, of course.

[JAL_1138]

Not exactly what OP describes, but I've used 1e character classes (including to-hit numbers and spells) with 2e combat rules and all other game mechanics. Or 1e modules, setting material, and/or monsters with 2e classes and all other game mechanics, or BECMI modules and/or monsters with 2e character classes and all other game mechanics.

None of them take all that much work to use with the others, under Level 20 (where AD&D stops and BECMI keeps going), since the numbers for HP, damage, saves, to-hit, and AC are all pretty similar, even if not precisely identical--the main conversion work is swapping out to-hit tables with THAC0, really, and those almost-but-not-quite match up anyway.

[ImNotTrevor]

To be honest, whenwhen someone invites me to a mishmash of systems like some of these suggest, that's usually my cue to be "too busy" for this particular campaign.

It's not really an aspersion I want to cast, but I find that 90% of the time these campaigns end up being...really weird and not running particularly well. Mostly because the systems involved don't actually have a united core to work with, thematically or otherwise, and so things just get weird and/or hiccup the whole way.

And once you're struggling to buuld enough adapters to make all this crap work together, you're basically building a system. Kinda. Frankensystem's monster.

I personally think that most of these goals can be accomplished with really light homebrew of one core system, with the exception of signifcant changes of scale.

For instance,

The Cyberspace Magical Opera could quite easily be run entirely out of Stars Without Number by adding a few additional skills for Cyberspace (and otherwise leave it narratively open) with a career/background that involves those new skills, and some expansions upon the Psychics to make them feel more magical than psychic. Everything else could stay equal. (Maybe the HP system changes to prevent more deaths, if that is important to you)

Otherwise? SWN could handle it pretty well. You may need to throw out the default storyline, but meh, that's easy. You just ignore it.

The SWN Sector Generator is an awesome tool for... really any space opera game. I highly recommend it. (Just google it, it should be the first thing that pops up.)

[JBPuffin]

I actually have this as a pie-in-the-sky goal: run a game based on a crapton of different systems running in tandem. It's a large part of my daydreaming, seeing this idea as an MMO of sorts...

[RazorChain]

My group once used Warhammer Fantasy Battle rules and miniatures to resolve a scenario where we were protecting a town from an Orcish horde and we were leading the army. We were playing AD&D 2nd. ed. at the time.

[wumpus]

Now you kids get off my lawn!

Somehow I think that old-school play (the gamemaster makes up the rules of the world on the fly, players are not consult on whatever those rules might be today) is pretty much mandatory for such things. Players that expect every rule written out and the gamemaster to follow them to the letter will disappointed.

Best game I ever played was Villains and Vigilantes with *absolutely* *no* idea what the rules were beyond character generation and a vague idea of what I needed to roll for my powers to work. Most of it was a brilliant GM, but I'm sure lack of complete knowledge of the world helped (I'm pretty sure said GM followed the rule of cool more than any rule in the book as well). See Mark Twain's lament about becoming a riverboat pilot.

[Tyrrell]

I did an Ars Magica vampire Dark Ages crossover game where Ars magica players used Ars Magica rules and Vampire players used vampire rules and I when they interacted I judged on the fly ("five successes is better than their defense total of 14" "three successes on your Dominate roll bounces off of their parma magica").

[TheIronGolem]

Cyberpunk 2020. Nice game, but it had a serious problem with regards to its hacking system - basically, for every turn the non-hackers get, the hacker plays a minigame with the DM that lasts several turns.

I had a DM once that sought to solve this problem by ditching the normal hacking rules in favor of the Netrunner card game that had just come out (not the one that came out a couple of years ago; this was the 90's when everyone was making me-too MTG clones). Then he wondered why we still had the same problems even though all he had done is make the non-hackers watch a different minigame play out between their turns.

[2D8HP]

Somehow I think that old-school play (the gamemaster makes up the rules of the world on the fly, players are not consult on whatever those rules might be today) is pretty much mandatory for such things. Players that expect every rule written out and the gamemaster to follow them to the letter will disappointed.

Best game I ever played was Villains and Vigilantes with *absolutely* *no* idea what the rules were beyond character generation and a vague idea of what I needed to roll for my powers to work. Most of it was a brilliant GM, but I'm sure lack of complete knowledge of the world helped (I'm pretty sure said GM followed the rule of cool more than any rule in the book as well). See Mark Twain's lament about becoming a riverboat pilot.

Wait. There's other ways to play?
Just seems so wrong. ..