JamesonCourage
Adventurer
That's a cool idea. The HP bonus based on size.My current system does 1st level hit points as HD+Con Bonus+Size Bonus (8 for a medium-sized creature). Since PC's at least get max hit points at first level as a result of being Heros, this means that PC's tend to have between 12 and 24 hit points at first level. Since they don't die until -10, and since most attacks do 1 die of damage, this tends to make them very durable. Tying the hit points to size also resolves the problem of famous house cat problem (too little distinction between a house cat and its owner) and other issues like the whale problem (large creatures requiring massive hit die to reflect their durability, but gaining all the other benefits of HD as well).
In my RPG, I also tried to tackle the issue, but I went about it through other methods. In my game, you deal +4 damage per size larger you are. So, cats might deal very little damage to most things (based on their natural attack), but they deal +4 damage to rats, say, almost killing / killing them instantly. And, in that vein, humans with clubs would kill rats, cats, and the like easily enough (+12 / +8 damage), with things like dogs being wounded easier, but not quite as easily (+4 damage for small dogs).
That said, I also have a feat that grants DR/ER against smaller creatures, and it's not uncommon for me to work it into races or creatures I make. Humans rarely take lethal wounds from cats; the DR protects them. If something can wound them past it, occasionally, that might be covered by a sort of armor penetration the creature possesses, or by a lucky critical attack (lack a cat honestly wounding a human, as compared to scratching the crap out of them).
But, like your solution (though drastically different in implementation), I also offer a feat that gives a bonus to HP based on size, but only per size above medium (I also often work this in racially to creatures or races). So, larger creatures can more easily be durable, and fight off smaller creatures, while also damaging smaller creatures more easily.
This is also something I thought about for my RPG. I allow bonus damage dice when beating AC (for each 5 you beat it by, roll another base damage die -no Str bonus, etc.), though that damage die is reduced by DR separately. So, if I attacked a deer's ACvS (AC vs Surprise, in my game, or flat-footed in 3.X, I think), its AC drops tremendously, and it's a lot easier for me to rack up those extra damage dice. Throw in an ability like sneak attack (and called shots, in my game), and you can take one down easily enough in one shot.It does however have a problem I haven't figured out what I'm going to do about and which I mentally refer to as the 'deer problem'. At an average of 12-24 hit points, first level characters can take on average 3d6 to 6d6 damage before even being in danger of dying. This means that in general, it's hard to one shot even a 1HD target without a critical hit. Thus, how do 1st level humans hunt game like deer? A 1HD animal is no longer threatened by a 1HD weapon. A 1HD soldier requires multiple attacks with 1HD weapons to stagger or kill. It hasn't been a huge problem of me, but it nags on me, and I can see why some people wouldn't want to put it into their game.
Not sure if that'd work in your game, though. I don't know if you have armor give damage reduction (it gives both DR and AC in my games), so the extra damage die thing gets iffy. And, you give HP based on size, and that's going to buff that deer up... maybe your Hunter class gets a coup de grace / auto crit / death attack ability with some sort of setup shot on flat-footed creatures, if it makes a successful check against them? I don't know your skills, but I'm thinking something like a Knowledge (nature) or Heal check, or something, for animals, if we're going by 3.X skills.
Anyways, this could easily be its own topic, even if not many people have much interest in it. Oh, how I miss the old House Rules sub-forum. So many interesting things in there. As always, play what you like
