My Anti weapons are Deiter, and Nahi...
i like the concept, of a - power, and - damage ability, it would never be very strong, but it would be affective.
it'd likely never exceed -2 which would be -2 power, -2 damage.
heres a nifty idea.
Ability = Transfer affect.
this would transfer any affect from you to them, or them to you depending.
so if you had poison, and they had +1 pill per round, the affect would transfer giving you +1 pill, and them poison
I like Chaos. in fact, perhaps Chaos would be a good name for the ability