iwatt said:
I'd just allow the same mechanic (- to hit trade for + to damage). Seems good enough for me when using an abstract hitpoint sytem liek DnD uses.
What I'd recommend is making the Power Attack mechanic the extension of the Called Shot mechanic in the same way that Combat Expertise is the extension of the Fighting Defensively mechanic.
To whit:
Anyone has the ability to take a -4 penalty to attacks in order to gain a +2 Dodge bonus to AC. 5 Ranks in Tumble can increase that to a -4 / +3 ratio.
A character can take the Combat Expertise feat, which allows them to trade penalties to attack and bonuses to AC at a 1-to-1 ratio, up to a limit of their BAB or -/+ 5, whichever is less.
The two may be used together.
For review:
Anyone has the ability to take a -4 penalty to attacks in order to gain a +2 bonus to damage rolls. This is a "Called Shot."
A character can take the Power Attack feat, which allows them to trade penalties to attack and bonuses to damage at a 1-to-1 ration, up to a limit of their BAB.
The two may be used together.
I'd also reimplement the 3.0 rule that Power Attack may be used with any weapon. I'd also likely include the 3.5 doubling of PA for two-handed weapons, because I don't see a need to change it for these purposes.