i’ve been playing around w/how to implement the greater 2-weapon fighting and perfect two-weapon fighting feats in nwn1. my first approach has been to use EffectModifyAttacks and penalizing the off-hand attack bonus to make up for the out-of-sequence attack bonuses used. however, this approach suffers from 2 disadvantages ;  the modifications don’t at all replicate the exact sequence expected from the SRD feats, and  in the case of perfect two-weapon fighting, the character’s ability to hit more difficult opponents is unfairly penalized. so i was wondering if anyone else might have an interesting approach.
my approach so far
the ‘textbook’ greater 2-weapon fighting BAB progression for a 1/1-stepped character at 20th level, assuming most favourable conditions, is
what we get w/EffectModifyAttacks alone is
i.e., the final attack on the off hand is at +12 more than it should be because it is at full BAB and ignores the off-hand penalty, effectively giving the character a +12 bonus to hit on the last attack.
what i’ve been doing to offset this is simply penalizing the off hand by -4, which results in
which is far from ideal, but works [well, basically…] in that although the higher attack in the off hand is penalized by 2, each of the other attacks are at +1. obviously, this does make opponents on the upper end of the scale harder to hit than they otherwise would be, but for squishier opponents, it’s an approach that seems to be a ‘reasonable’ compromise, both to me and to my players.
but perfect two-weapon fighting is a different story, since the skew is so much more pronounced. here, the progression should be
but w/EffectModifyAttacks alone, it’s actually
i.e., not one but two attacks per round receive a de facto +12 bonus to hit! and unfortunately, applying a penalty to the off-hand here becomes so draconic as to be unworkable ; it would virtually guarantee that opponents w/higher ac’s would never be hit by off-hand attacks, where they would be w/the real feat.
so, what do you think ? is trying to implement these feats in nwn1 a fool’s errand ? or can you see a way to make it work ?