Fusion spells and multi-techs in this game, while definitely extremely strong, are limited to Commander Mode and cannot be used normally -- swap Ellen into the 'Bench' spot on your party and go into battle to play around with it a little bit. It makes formations, loadout, and position more important, but you give up fine tuned control for it; Sarah is a really good character to use if you do a later run and want to play through with it.