In my game Aptos Adventures (Rpgm 2003), a pair of twins can do dual attacks.
What I want is to make it so the other twin's battle graphic
disappears when this skill is used (the one who uses it
disappears as the battle animation of them attacking is shown).
I guess I could do this with classes but how would you trigger
it when the skill is used?

It worked! in the battle events, when the skill is used it inflicts a temporary condition that turns the other twin invisible
and then turns them back! But now I have to separate the twin category to just these skills (before under this category they had their own unique skills as well)

Well, the problem seems to be solved but there is a simpler way.
I'll tell it anyways: http://img706.imageshack.us/i/durrhurr.png/
So in a nutshell, when you choose a pose for your skills, just choose a blank pose that has no animation whatsoever.
Eliminates the need for battle events.

Yeah but that only makes the one using the skill disappear