View Full Version : Building my own system, looking for advice. (d20/???)

2011-10-15, 05:48 AM
So, let me set this up for you.

I'm writing a fiction series, which I'm still working out the execution for, be it webcomic, web-animation, or whatever else. (I favor animation, but a webcomic development in the interim seems like a good way to bring in attention while I undergo the much lengthier production.) The series is urban fantasy, in both the current trend and the literal sense. I've got vampires, werewolves, and demons, but also goblins, dragons, trolls, elves, dwarves, satyrs, mythology, magic, etc.

Being a gamer, though, I'm building this world from the ground up, with a sense of logic and consistency. Connections are tenuous at times, but taking a few key jumps in logic, everything works together, with physics, chemistry, and biology all in consideration.

The basic story concept is that, okay, Magic is real, but when you use it (or OVER-use it in many cases) it changes you. Spirits of magic can create magical effects in response to rituals, or you can more directly harness them to gain their powers, at a risk. The more you use their magic, the more they return the favor by gradually transforming you to express their related traits (called deviations), which are often animalistic in nature.

Over time, in the past, this created the various monsters, especially if someone went too far, losing themselves in their instincts. Speciation divided the various groups, making them vulnerable to mundane human persecution. Some groups died out, others used magic to hide their children in human form, unable to wipe clean the taint of magic on their genes. These children, if exposed to magics, would re-awaken, rapidly mutating into their ancestors' forms. Centuries later, we have modern humans, unknowing descendants of monsters, coming into accidental contact with magic and expressing their ancestral deviations and magical powers, which are not only addictive, but dangerous, making them all the more tasty to the predators of the old world, like vampires, demons, and who knows what else.

I'm building a roleplaying system to represent the world, and help me flesh out the available options for characters. My main experiences have been in D&D, 3rd and 4th editions, (plus d20 modern) but also some WoD (I own all the new world core books, though werewolf was the only one I've looked through extensively, aside from character basics), and some others here and there. I've not played it but I like the story-centric aspects of the Dresden Files RPG. I looked at the basics for GURPS years ago, but it's been 4 or 5 years since I've looked at them in any depth, and I never played.

I've tried retrofitting both d20 modern and WoD to suit my setting, with mixed results. Now I want to try something a little more from scratch, but there's a lot of elements I'm borrowing in from both D&D and WoD.

I will mention, in several places I refer to common terms for ease of reference, but I could change them to suit my needs. (one example is feats. d20 uses the term feat, but the same concept in WoD is the talent, and I'm sure other similar abilities have a variety of names in other systems.)

Core Mechanics:
I'm debating between using a d10 and a d20 as my core dice mechanic, or perhaps something else (3d6?). I want to keep it conceptually simple, using only a basic dice+mods style roll.

The debated point here is, does using a d20 make a game a d20-system game? How much does it take to be called a 'd20 game', and is that a good or bad thing?
Depending on what I use as my core dice mechanic, I'm currently looking at several different botch and crit possibilities.

I'm currently debating options, but the basic idea for a crit-fail (min-roll being an auto-fail) seems to be fairly standard. I see little reason to change it, and I've got some ideas for playing with the base version as character mechanics. (for instance, a certain penalty might modify the die roll directly, meaning the crit-fail number might be expanded, or a specific bonus might keep it from being hit at all.)
I also like the idea of the unlimited upper-end style of exceptional rolling. It makes it possible for anything to happen, but it doesn't mean that there's a flat 1-in-20 chance for 'anything' to always succeed. Which method I use depends on the dice I settle on. If I use a d10, a 10 on the die would let you roll an extra d10 and add it to the roll result. If I go with a d20, I'm thinking either a 20 or even a 19-20 would allow you to roll an extra d10 to add in. If I do something else, like doing 3d6, it might be something like if you roll a 6 on any single die, roll that die again and add it to the result. In all cases, the max number on the extra die would continue the expanded rolling. Chances get more remote, but not impossible.
In place of a normal nat-20=auto-success type of mechanic, I want to make use of the expanding upper rolls by some simple math. If the roll attempt succeeds, however much it exceeds the base DC(/AC/etc) by, is rolled into the effect. Most commonly, this excess number on an attack is rolled over into the damage, but it might also figure into other uses, like a skill's effectiveness, or a spell's duration, etc.

Well, the obvious meaning is that dice rolls are a little less mindless. Some people might complain that adding in the extra effect-rollover is an extra bit of math they don't want to deal with during gaming. I agree it is a little extra to think about, but I think it's simple enough math that either party in a given exchange could do it. Maybe I've gamed with too many engineers, but if people can handle doing the math for Power Attack on the fly, this is no different.
Now, the last core concept I want to mention up front, I want to use a small-total, free-spending XP system. Functionally, this would be very similar to (new) World of Darkness's system, where you can spend your XP on whatever you like. In my concept, ability scores, class levels, feats, skill focuses (explained below), and skill tricks/maneuvers are all purchasable.

The main issue here is that I'd like to keep character progression mechanically unique. Neither concept is really better, they just have situational advantages. In effect, using an XP-buy system lets you build a character very free-form, almost akin to building a monster in 4e D&D, you can assign extra feats and powers to a character as desired, without worrying about if he has exactly the number of feats an X-HD creature should have.

Character Stats and Bonuses
There's two components to this, the basic ability scores, and the result stats and traits.

I set up my ability scores in a sort of hybrid analogy between D&D and WoD. I use the Power/Finesse/Resistance model from nWoD, but split across only Physical and Mental abilities, which are comparable to the core six d20 stats, but slightly different. (notably, I changed names to try and keep unique first letters for each.)

Strength - Used for Melee/Bow damage, carry capacity, and adds to your speed.
Agility - Used as the bonus for ALL attack checks of a physical nature, and bonus to the Dodge trait. (this split represents the basic idea that it doesn't matter how strong you are, if you're too slow to make contact, it won't matter)
Endurance - Bonus to health points per level, and bonus to Tough trait.
Intellect - Bonus damage for spells and guns (representing intellect's role in choice accuracy and precision striking), and extra skill points per class level
Charisma - Bonus energy points per level, and roll-to-hit bonus for spells
Resolve - Bonus to Will trait, adds to Initiative, and used in secondary saving rolls for spell effects (basically as the generic bonus-to-spell-DC on secondary effects)

The basic idea here is that all these stats should be useful to anyone, and if you want to dump one or more, it should be a difficult decision, but not a crippling one. The MAD spread here is intentional, and means that you'll have different techniques for combat. Maybe Character A excels in hard first strikes, but has little endurance, while character B is slower, less accurate, but can outlast their opponents and eventually catch them in exhaustion. Instead of these varied styles of play being forced by the mechanics of different classes, they're choices in character. Two characters on relatively the same path could play very differently just based on their ability scores alone.

The basic issue here is whether to use a direct/indirect numeric split. Currently, along with my other d20-borrowed rules, I'm favoring using the average of 10 = +0 bonus, same as standard D&D/d20. I tried setting up a direct-number relationship at first, but the numbers felt like they were getting too big too quick, because I want more granularity than the WoD's 1-5 mundane range, but using a 1-10 mundane range makes the rest of the dice involved feel insignificant.

The above ability scores are used to figure out the resulting character stats. So, to explain some of the above:

Health (HP) This comes in three pools, body, lethal, and nonlethal. Body is the critical health, lose that and you're dead. Lethal is a majority of damage, but nonlethal should more impact than in regular D&D. My current basic concept is the Wound/Vitality points in d20 star wars (pre-saga edition) and/or the UA variant of the same name.
Energy (EP) Used for various mechanics, energy can be spent to gain extra actions in combat, boost combat maneuvers, and cast spells. Specifically, energy can be subdivided into two forms of magic-only energy points, which have specific casting purposes.

The next five mechanics are derived from stats, but are also dependent on if/how I implement class mechanics, which I'll explain below. (HP and EP too, but these five are only split from the ability score which boosts them by the class bonuses, as of now.)

Combat Bonus - The basic attack bonus. Anything that is directly offensive in nature, including weapon attacks, combat maneuvers, and some attack spells, uses this value.
Special Bonus - This is for anything else that's left, generally when done in combat. This includes in-combat skill usage, casting spells, and so forth. Magic effects also use this number to get their numeric effect, making this almost act like a unified caster level. (the two uses also interact, meaning that you have decide between such number of bonus giving you that number of dice in spell damage, and subtracting that number from the effective DC value. Rough example: you start with a 3d6 fireball with a 13 DC. You can trade that to be a 6d6 fireball with a 10 DC, or a 1d6 fireball with a 15 DC.)

The next three are similar to d20 saves, but I can see them being used a lot of different ways, and I do, even now, like as bonus to rolls (like a 3.5 save), flat numbers (like a 4e defense, 10+number), or even just as a given number to use directly.
Dodge - Similar to the d20 concept of Reflex (and touch AC), Dodge is the basic does-it-hit-me? value. Basic defense number is 10+dodge.
Tough - Similar to d20 Fortitude, Tough is the stat which covers stability, resilience versus poison effects, and also used as an inherent damage-reduction value. (like if your Tough is +3, and you get hit, subtract 3 from the damage total.)
Will - Similar to d20 Will, this version of Will is used as the resistance to social effects, psychic effects, and as the direct counter to my basic character-degradation mechanic, Instinct.

Instinct - In almost all cases, Instinct acts as a bonus to Will checks, and can be situationally added to various other checks (rage effects, mainly), but it's actually a self-defeating trap mechanism as well. Instinct increases when a character becomes more monstrous, and under specific circumstances, they will need to make a self-opposed check, Will vs. Instinct, to keep control of themselves. (This is conceptually inherited from nWoD games, where the emphasis in the books seemed to be as much the horror of losing oneself as their surroundings.)
Skill points - I'll go into this below, but my current skill system has three main components, skill points (which go with classes, explained below), which are flat-spent, skill focuses, which have cumulative cost, and skill tricks, which aren't so much added in as outgrowths of the progression, adding extra special extra actions you can do. Mainly, this is because the total skill bonus itself doesn't let you do anything but make Knowledge checks. It's the tricks that actually let you do something with any given skill.

Class Mechanics
So, as I mention above, I'm fairly stuck on the idea of using class progressions. I'm not married to the idea, though. Especially if I decided to shift this away from d20 mechanics, I could see breaking down these class bonuses into a series of other abilities which progressed in a different manner, like a series of feat-stages or something.

Right now, I'm using 10-level classes, but I want to clarify, this doesn't mean I'm using a 10-level cap. My closest example is d20 modern, where they also had 10-level classes, but used a functional 20-level cap. Strictly speaking, I'm not building in ANY kind of cap, especially since I'm trying to keep the gains for each level fairly minimal, to allow mixed-level groups to keep functional. I want this to be a fairly free-flowing class system. Right now, I could even kill the pre-existing 10-level limit per class, and structure these classes more akin to 3.5 epic classes, with no functional limit. (I really don't want to do that, but the current number of levels is arbitrary.)

I like using d20-style classes as the idea of taking the concept of a path of progression, specifically the aspect of 3rd edition/d20 modern multiclassing, being able to dabble here and there in different classes and concepts to create depth and dimensionality in a character's abilities. (nWoD doesn't allow mixing of the gamebooks, mostly because they're conceptually separate, but it always made me curious about how it worked, assuming the basic concepts of power progression are similar in oWoD, when you wound up with a hybrid creature, rare and abominable as they were.)
The above also means I like using class-granted hit points/dice, though I prefer to keep the difference between 1st and 10th level characters fairly low via a high starting value ala D&D 4e.
Right now my progressions for the Combat and Special bonuses vary: 1/4 level, 1/2 level, 3/4 level, full level. The Dodge/Tough/Will traits have a high, medium, and low track. Rounding down: low is 1/3 + (1/3 level), medium is 1/2 + (1/2 level), and high is 2/3 + (2/3 level).

Other Character Components
The basic idea of using feats/talents is more or less a no-brainer, though whether to use a single-value feat (d20) or a variable-cost talent(WoD) is something I'm not sure about. (Right now, I'm favoring the first, just for keeping my variables-I-have-to-keep-in-balance down.)

My current system is to have class levels grant skill points which can be spent 1 for 1, capped at your total level in all classes, but that you can also buy a focus directly, using XP, which is uncapped. (I'm thinking you could also buy extra focuses as specialities for certain situations, like knowing one particular sub-field of a science really well, or having exceptional skill with only one particular type of weapon that isn't transferrable to other kinds. Thus, this second type of specialty bonus would stack with your basic focus and your ranks at the cost of specialization.)

Skills themselves aren't used directly, they represent training and knowledge of any kind, from sciences to firearms to melee weapons, but they're only rolled directly for knowledge checks. For active skills, they merely enable special bonuses or extra techniques. Like for instance, you have an Athletics skill, but it doesn't let you jump better (that's probably just a basic d20+Strength+Agility roll), it instead grants you the ability to perform some kind of athletic special maneuver incorporating other bonuses, like a unique leap, that might let you add your Special bonus to your aforementioned d20+str+agl roll, or to formulate those numbers in a different way (as yards versus feet traveled, for instance). (Basically, I think of it like 4e's Skill Utilities. The idea being that the ability to 'Jump' might be a granted ability of Athletics training, with better versions available at higher ranks. The skill itself is training/knowledge, but it grants useable 'powers' along the way.)

Specifically, I also have what I refer to as 'action skills', which include firearms, brawling, weaponry, demolitions, etc. (similar to Linguistics in Pathfinder, ranks in a weapon skill grant extra proficiency along the way, which are also buyable directly with XP). Because your Combat modifier is only your general how-well-you-handle-yourself, rather than your skill with any particular kind of weapons, it's simply the cap for your ability.

So, for instance, Firearms as a skill rank total (including various bonuses, in this case Dex) might have you at +9. In contrast, your Weaponry skill (including Endurance, in this case) is only at +4. Your Combat bonus (plus Dex) is at a +7. When using a gun, you would be making attacks at +7, because while skilled, your combat training is only so good. (maybe you've trained in a gun range and know how to handle and clean a weapon, but rarely seen active firefights.) If you picked up a sword, because you've only barely had hand-to-hand weapons training, you're at a significant disadvantage.

Now, the main advantage of this kind of concept is simulationism. Weapons don't become a binary yes/no like in D&D, instead it has flavor and nuance. It does mean there's a little more to track, but the bonus should be easy enough to figure once and write a passive number that doesn't need to change. This also folds in stuff like Weapon Focus.

Miscellaneous Other System Bits
I'm considering the idea of using a defense roll in addition to an attack roll, because it gives the defender the option to use a parry or shield technique instead of just receiving the hit.

Something else I've decided is that my basic dice rolls for hit points are actually daily totals. You don't actually start your playing day with full hit points, you roll your hit dice and add your bonuses, averaging at starting a day with 70-80% totals. You actual cap total would be the maximized die+bonuses. I've also got a basic relative-value healing idea, much like a 4e healing surge, where a short recovery, like a Second Wind style ability, would have you take one of your highest-size hit dice (so for instance, someone with 4d6+2d8+3d10 would grab the d10) and gain that much (+endurance mod), giving an advantage to heftier-diced characters. The fact that I'm using an energy die in the same fashion means that one could have a short post-combat rest regaining one hit die and one energy die afterwards, giving longevity to a character's points in a day.

Another different than standard concept. The idea here being that I don't like relying on a random number for something that has major impact on your character. This way, the maxed total is what you actually gain, but the rolled number has some daily impact as well. I feel like it's a good tradeoff that shares both the 3e and 4e concepts of HP gain. Now if only I could figure a way to make my players less obsessed with starting each day with full HP..

I also really like the Dresden Files' idea of story concepts for your character that your GM can push for you to influence your actions for a reward. It play similar to the WoD morality system, as well as some of the variants of that system in the WoD Mirrors book. (Very cool book, it's the Unearthed Arcana for the nWoD. I recommend it to anybody who likes the WoD concepts but wants to see more from the system in other areas. I loved the social-combat system they explored in that.) I'm thinking I might use a basic character-concepts core like that to be able to offer midgame XP. (but then that's also why I'd like to keep all my mechanical units relatively compact, for on-the-fly purchase.)

Legal stuff and d20 system debates, redux.
My current biggest problem is, I'm not sure how much of this is direct cloning from only one source, or if it's generic enough that I'm not stepping on legal toes. I make a lot of comparisons here for clarity's sake, but in my own documents I've tried to explain it from a newcomer's standpoint, without other brand references. (My biggest concern is that while my dodge/tough/will set started as a basic reflection of fort/ref/will, it's grown on me into something else representing concepts on a separate level from the old trio, really as the core of my system.)

I'm also not sure if I should make this a d20-system game, or something else. (I already mentioned my basic dice-roll question) At first, I was trying to use a 1-to-1 ability score value system, but because I want to use hit dice and such, the numbers start to pile up, because I want more granularity than WoD's 1-5 mundane ability range. d20 has the convenience of offering the base-10 ability average, with the ability bonus providing a standard of numbers that is much more friendly to play with without ballooning numbers too quickly. On the other hand, aside from the fact that I use 6 ability scores, use a d20 for my basic rolls, and I generally use escalating numbers, everything else is different. If I do this d20, I can use the term 'Feat', but otherwise it's going to be talent or trick or something else. Everything else is entirely new or otherwise generic. (I don't even plan on using Power Attack!)

Honestly, when I go through it, it half reads like I'm trying to write a comprehensive d20 game that takes into account all the development concepts for the whole length of 3e/3.5, and some of 4th, and build it into a new version of d20 modern that takes Modern's core differences from straight D&D, and runs with them. (Which would be cool, but probably not what WotC has in mind. Plus all the core system stuff is built on my world, not their Urban Arcana or any other of their previous settings.)

I'm not mentioning it here, but a good portion of my theoretical balance rides on the universe-specific mechanics I haven't yet enumerated here. So yeah, there's a lot of stuff here, and it's kind of a mess to explain. I tried to expound the basic principles, but if anybody has any questions, feel free to ask.

Thanks for taking the time to look through this. :D

2011-10-16, 03:35 AM
Okay, so, nobody has said a word, and I don't want this to go quietly into that second-page goodnight..

So let me start explaining my current character and class concepts. I'll also try to explain some of the character archetypes and world/system concepts that go into the development.

Just to start, I have three basic action types, Basic, Move, and Verbal. (Talking is not a free action!) You can also spend energy to take extra actions in a round, both reflexively (allowing defensive maneuvers) and once per round on your turn, allowing you to get an extra action on your turn.

Currently, all classes are 10 levels long. I might expand this, but right now it works as a starting point. (My classes are all incremental, meaning they have options which generally just scale up with further class levels.) Expanding them to 15 or 20-level classes (or condensing them into 5-level chunklettes) is currently no problem.

My four main starting classes are all mundane. As with 4e's Martial powersource, trying to cover all roles in purely mundane fashion is damned hard. So I mellowed them out a bit, and went with a more mundane approach to each general concept, without locking someone taking any one class out of pursuing one of the other roles later.

Brawler - Currently the closest thing to a Tank/Defender archetype, at least in the sack'o'HP model. High health, high combat bonus, good Tough trait, but lowest Special bonus, few skill points and a low Will trait. Gets 'Brawl', an unarmed combat feat (unarmed strikes deal lethal, threatens 2 yards instead of just 1, fist deals larger dice). Main ability is Brutal Strike (trade -2 to combat bonus for +1d6 damage until end of round, increasing every 2nd Brawler level)
Expert - The skill-monkey class. High skill poins, and has the highest Special bonus amongst the mundane classes, making the best in-combat skill user, and the best potential spellcaster. Gets a feat that lets him take 10 on all skill checks while in combat, 'Grace Under Pressure'. Main ability is a floating +1 per every 2nd Expert level, added to a skill chosen per day, which stacks with all other skill bonuses.
Leader - The support/commander class. Pretty good bonuses across the board, upper-middle of the possible range. Gets a feat that lets him spend his own verbal action and some energy to allow an ally to take an extra action (basically a warning shout or a command to act). His main ability is an improving bonus to his allies' attacks, defenses, damage, or a trained skill, which improves every 2nd Leader level.
Sneak - Rather than reflecting the D&D rogue(and by that I mean low-accuracy, but high potential damage in a sneak attack), my Sneak is a quick fighting type, with a full combat bonus, the dual-wielding feat, and the ability to make a flurry of strikes as a single basic action, basically subtracting -2 from all attacks but gaining an extra attack per every 2nd Sneak level (so by 10th level, he could choose to make 6 attacks, but they're all at a -10 bonus, or if combined with the dual-wielding, 12 attacks, but at a -12 or -16 penalty.)

Honestly, my biggest question is, should I make this a d20-based game? Are there other options that have the same kind of granularity I mention in the OP, or that have the same easy-to-use dice resolution mechanics? Does using a d20 and base-10 stats even make it a d20 game, if that's the closest thing to regular D&D left in the mechanics?

I've got a bunch more classes (the above four are the mundane bases, from here on out we get more magical in nature), so if somebody doesn't say anything I'll keep droning on with my stuff forever and ever and ever...

...and ever and ever...


2011-10-16, 04:45 AM
Would it make it easier on anyone if I posted a doc/pdf? (Currently I'm working from a private wiki) I'm trying to keep my descriptions filled with relative references, to give my choices context, and allow you to consider alternatives, whereas if I started posting straight game text, it might get a bit hard to jump into and still understand the what/why/how. There's some of this stuff I have multiple versions of because I haven't been able to decide between different options. Presently on my wiki, I'm doubling about a third of the pages with a (d20) tag, just for the sake of posting up d20-like versions of classes as compared to a more scattered mechanic I've not really figured out yet.

(I'm not trying to self-bump, just evoke some feedback. Give me something to work with, please!)

2011-10-16, 07:04 AM
At a glance, an evident problem with this post is that things are too clunky.
1. Put line breaks between paragraphs
2. Use enlarged and bold topic-titles.
3. Try to supply motivations to each of your proposed mechanics beyond "that's how I'd like it to be".
4. Try to re-evaluate the pros & cans of each of your rules gameflow-wise.

2011-10-16, 12:42 PM
Sort of a lot to absorb (I will re-read and try to be more constructive), but the main question seems to be about the dice mechanic. While reading this, I came up with an idea; not sure if it's what you want, but it avoids having large numbers of dice while having a more bell-curved shape than straight d20. It also allows for low level characters to do as well as high level characters, but it's harder for them. It's geared towards your ten level classes/tenth being the highest level, but could probably be modified. Working title for the system is Right between the Eyes because 1,1 (snake eyes) is the best possible rolls.

Essentially, you have dice that represent your inaccuracy/miss chance and these dice reduce as you progress.
{table=head]Lvl | Miss dice
1st | 2d12
2nd | d12+d10
3rd | 2d10
4th | d10+d8
5th | 2d8
6th | d8+d6
7th | 2d6
8th | d6+d4
9th | 2d4
10th | d4+d3
So, you'd roll 24-your miss dice. Maximum possible roll, then is a 22 and the minimum is 0, with an average of 11. Minimum and average are for a first level character. As you progress, the minimum and average increase, representing that higher level characters are generally better at doing things than lower level characters. It is possible for low level characters to do as well (since anyone can roll a 22), but it's more difficult for them. Just a thought; not sure if it's at all applicable.

2011-10-20, 05:31 AM
Okay, re-wrote and formatted my first post for clarity. Mostly in the first half, pretty much re-wrote it. The second half is basically just titled off, but it's after 6 in the freakin' AM and I need some sleep.

Playswithfire, I appreciate the idea, but that dice system isn't really compatible with what I'm doing, and it's a little complex for my needs. (I'm not using a level cap of 10, just limiting each class to 10 levels. Multiclassing is encouraged if not required, and I currently have no level cap.)

Smokin Red
2011-10-20, 06:37 AM
The debated point here is, does using a d20 make a game a d20-system game? How much does it take to be called a 'd20 game', and is that a good or bad thing?

I really can't contribute that much (and as I'm currently 'working' I have no time to read all your stuff now).

But, I know at least one other system (aside from the usual d20) that uses a d20 as core-dice. (look here (http://en.wikipedia.org/wiki/The_Dark_Eye#Resolution_of_actions) if interested)
So, no, your system doesn't have to be d20.
(If that's good or bad depends on your, or the beholders view)

2011-10-21, 03:58 AM
The more I think about it, if I decide to not use a d20 for my basic dice mechanic, a 3d6 w/exploding 6's seems like the friendliest set.

I ran the math, as best I could. On the base 3d6, 10.5 is the average value, equalling a basic take-10 for most purposes. But the exploding 6 sets the actual average at about 12.444, give or take. (Feel free to prove me wrong, my math in this regard isn't the most accurate.) I sat for a few minutes on a dice roller and ran the numbers, I hit a pretty good spread, averaging around 8-16 on most rolls, but going up to as high as about 28 on the best roll so far.

I like this spread of numbers, it makes the dice feel effective, it does favor average numbers overall, but has some room for growth and luck to carry above and beyond expectations. That random chance that favors high ranges also means that a basic take-10 has some disadvantages. (which also means I can say that your basic defense number, 10+value, like with AC and 4e defenses, is on the slightly weaker end, making a defense roll, which I like, a viable and attractive option without forcing it on a less cooperative player or an overloaded GM.)