Switching to an earlier topic, how would you model reach in an RPG? 3e had AoOs, 4e has threatening reach, but those only worked for giants vs. men. What about spear vs. knife?
I like the way it is done in the Codex Martialis. There are three range categories: Onset, Melee, and Grapple.
Two of those ranges are already in d20 3.5 games: Melee and Grapple (Grapple range is inside the same square as your opponent).
Onset is used for the fist attack in a melee, but after that, a character has to try to maintain some distance from his opponent if he has a long weapon (kind of like a reach weapon in a d20 game). The spearman would want to maintain Onset range, while the character with the dagger would prefer either Melee or Grapple range.
Mechanically, how this is done in the game is that the weapon is given attack bonuses/penalties a different ranges.
For example....
One-Handed Hunting Spear: +4 to hit at Onset Range; -4 to hit at Melee Range; +2 to Defense.
A typical small dagger: -4 to hit at Onset Range; +2 to hit at Melee Range; -4 to Defense.
So, the spearman will keep trying to keep the range at Onset between himself and the fighter using the dagger. At Onset range, the spearman is +4 to hit and +2 to his AC.
At that range, the dagger user is -4 to hit and -4 to Defense.
Thus, the dagger user will try to get in close, under the spearman's guard. He wants to keep the range at Melee--or even go into Grapple range where the dagger can be used but the spear cannot.
At Melee range, the dagger user has the advantage. He's +2 to hit (the spearman is -4 to hit).
I think that's a pretty good way to integrate the concept with the d20 system. Wish I had thought of it first.
Should you just always get an OA if someone attacks you with a weapon that's shorter than yours?
Is that how it's handled in 3E (or 4E?) D&D? Since I play the Conan game, some of the D&D rules are sketchy to me.
This is handled in Conan, and it's handled in a similar manner that the Codex addresses these issues.
In Conan, it's a +1 bonus to defence for the longer weapon, per weapon category, and it's a -1 penalty to defense for the shorter weapon, per weapon category: Light, One-Handed, Two-handed.
There is no penalty or bonus if the weapons are from the same category.
If there is a one-step difference in category, the user of the smaller weapon receives a -1 AC plenalty while his foe gets a +1 AC bonus.
If there is a two-step difference, the bonus and penalty increases to +2/-2 AC.
Thus, if a character with a dagger (Light weapon) is fighting a foe with a greatsword (Two-Handed weapon), the dagger user would be -2 AC and the greatsword bearer would be +2 AC.
In our situation above, with the one-handed spearman vs. the dagger wielder, the dagger dude would have -1 AC and the spearman would get +1 AC.