Thoughts on Size Categories

[Stellar_Magic]

For over a year I've been working on a D20 derived RPG system that was setup from the start to handle most everything (similar to how D20 modern has splat books for everything). Things have been going pretty good, except for one thing: Size Categories.

One thing I decided to eject from D20 and DnD was the idea of size categories providing a specific modifier to ability scores (most often strength to increase damage or dexterity to reduce AC). In DnD this meant that a player had to recalculate their strength score when under spells that increased their size and so forth...

Instead I came up with an alternative... increasing Multipliers for damage and hitpoints for larger sizes. So a medium size shark does 1d6 bite damage, a large size shark does 1d6x2 bit damage and 2x the hitpoints, a huge size shark does 1d6x5 bite damage and has 5x the hitpoints, a gargantuan size shark does 1d6x10 bite damage and has 10x the hitpoints, and a colossal shark does 1d6x20 bite damage and has 20x the hitpoints.

To balance this... for every size category above medium, the creature takes a -5 size penalty to attack rolls and AC.

This seems to work great up until around Huge size... as I'm getting negative values for Armor Class if I go to Gargantuan size. How do people feel about negative values for AC in a 3.5 derivative?

[Bruno Carvalho]

This seems to work great up until around Huge size... as I'm getting negative values for Armor Class if I go to Gargantuan size. How do people feel about negative values for AC in a 3.5 derivative?

What it means? That everyone will be able to hit 'em? So why bother giving them an AC after all? Just rule that in such sizes, every attack against AC is auto-hit, without rolling.

In other words: Pretty much awful.

[Lvl 2 Expert]

I've been working on something similar recently (weeks rather than your year), although it kind of got out of hand and started turning into a whole new (but simple and limited) system. The first thing I did is make the base stat points logarithmic rather than (sort of but not really the d&d system is kind of vague about this stuff) linear. Every two points you gain in a stat mean you've gotten twice as good at it. DC's have to be scaled accordingly. (I'm using something smaller than D20's for this system.) This way the stat points and any other statistic can effortlessly drop below zero, because there is no value for "no strength/intelligence/whatever at all. They just keep getting smaller and smaller.

I've decided to use twice as many size categories as D&D, so a step up makes a creature root(2) taller and root(8)=2root(2) heavier. In this process they gain 2 points of strength and constitution (a good case can be made for constitution being a third power function rather than second, but I quickly decided it has to scale with strength) and lose one point of agility (dexterity, which is used for hit and dodge chance in this system).

Another thing I'm probably going to end up doing is giving every character the same amount of hitpoints. Constitution will instead determine how much damage you take, the constitution of the target functions as the DC for the damage check. The formula will probably be something like (root(2)^((Str+some modifier)-(Con+some modifier)))*10 which can also be written as 2^(((Str+some modifier)-(Con+some modifier))/2)*10. (Too complicated to be ideal, but the system guide will include a handy list of powers of 2 and root 2 so you don't have to constantly grab your calculator.)



But as for the solution you picked: I don't think negative values for AC are a problem at all. As long as they still mean something in game. If everything with armor class 0 or below is an automatic hit to anyone, just give all the really big creatures armor class 0.

What might concern me a little more is that the damage and hitpoints of these creatures increase in the same pace as the creatures size, twice as long is twice as much damage. But the penalty to hit and armor class has a different pace, -5 for every step. This doesn't have to be a problem at all, since damage and hit chance are not directly related, but it's probably a good idea to do some test calculations on this stuff, how often creatures of different sizes hit each other and how much damage they're going to do to each other on average per hit as well as per turn (counting the misses). See if you like the results, if they feel natural. If they do, great job!

[Stellar_Magic]

Honestly, I'm not happy with the -5 penalty per size category to AC. Without doing that the -5 penalty per size category for attack rolls kind of falls to pieces though, as a -20 for a Colossal creature just doesn't seem to work. I need to make it so a bigger creature has a much harder time hitting a smaller creature, but this system really feels awfully clunky.

Hmm... I could steal a mechanic from Saga Edition. That has it so really big weapons like Turbolasers incurred a -20 penalty on attacking ships smaller than Colossal. This would mean that a Medium creature would have a -20 penalty to attacking creatures tiny size or smaller.... or a Huge creature would have a -20 penalty to attacking creatures Medium size or smaller.

That probably would work better.


What might concern me a little more is that the damage and hitpoints of these creatures increase in the same pace as the creatures size, twice as long is twice as much damage. But the penalty to hit and armor class has a different pace, -5 for every step. This doesn't have to be a problem at all, since damage and hit chance are not directly related, but it's probably a good idea to do some test calculations on this stuff, how often creatures of different sizes hit each other and how much damage they're going to do to each other on average per hit as well as per turn (counting the misses). See if you like the results, if they feel natural. If they do, great job!

It worked... but it lacks verisimilitude, and it really didn't seem to balance being little verses being big.

[SkipSandwich]

If you want multipliers INSTEAD of stat increases, we need to look at how that would actually play out by removing the stat modifiers.

Lets look at how a T-Rex would be affected by this change

Normal non-advanced T-Rex are size Huge with 18d8 HD with a Con of 21 (+5) and 3xToughness (+9) giving them about 180HP (Average) or 243 (Max)
AC is 14 (-2 size, +1 (Dex 12), +5 natural)
Bite attack bonus is +20 (+13 BAB + 9 Str - 2 Size)
They have a Bite that deals 3d6 base damage with a Str of 28 (+9), as their only attack it gains 1.5x multiplier for 3d6 + 13 final damage (average 24 damage, max 31)
Compared to a hypothetical medium sized baby T-Rex they have +16 Str, +8 Con, -4 Dex and +5 natural armor from size

Under the new proposed system the T-Rex's Con is reduced by 8 to become 13 (+1) reducing their base HP to 90 which is then multiplied by the huge modifier x5 to become 450
Bite damage is reduced 2 sizes from 3d6 down to 1d8, and Str is reduced from 28 - 16 to become 12 (+1), base damage is (1d8+1) x5 (average 27 damage, max 45)
Dex raises by 4 to become 16 (+3), natural armor goes down by 5 (+0) and flat size modifier is removed, final AC becomes 13
Bite attack bonus is +14 (+13 BAB +1 Str)

So comparatively, the new T-Rex is more then twice as hard to beat down through HP damage, but has a much lower Fort Save of +12 versus the old +16, notably, the T-Rex gains +15HP per instance of the Toughness feat.
They deal slightly more damage on average, but have a significantly lower Attack Bonus (-6 from standard)
AC is pretty much unchanged, only lower by 1 point from standard

In conclusion, at least for this monster, the only clear advantage is the extra hp they gain, the slightly higher average damage from multiplication is negated by the lower to-hit chance from the lowered base stats and AC is not significantly affected. Now, it's a different story once you start adding buffs such as from templates or ability enhancement spells like bull strength. +4 str to the new T-Rex ups them to Str 16 giving them +2 to-hit from higher strength and an a bite that deals effectively 5d8 +25 (average 47, max 65)