catnip is a wonderful item and probably one of the best in ANY FF game. the reason you give it to a gunner is because once you have trigger happy LV3 you can shot trout loads of times. so when your gunner, who doesnt have much HP anyway, goes into the yellow, use trigger happy and each shot will inflict 9999
this basically means with careful tactics you can beat almost ANY villian in the FF game.

but to get it, you have to beat the dark elemental, no easy task you may find. i was stupid enough to read the guide, so i did several attempts but my team was only on level fifty and flare nocked 9999 off, while ultima killed everyone.
.
.
.
theres an easy way to win tho, with pain as a dark knight, make sure your white mage goes first and cast reflect. if he casts flare it will reflect and destroy him, if he uses ultima, kiss your butt good by and try again, it's worth it