My favorite spell is Orthrus. Medusa is great but Orthrus cuts through tower shields with a weak attack, and then delivers a strong attack to the enemy. Excellent for facing ice enemies in Celestia.
It can be any spell in the game including traps and such
My favorite spells are backdraft and bull, one after the other since they do insane amounts of damage together. You could say ffa but I like the aoe persona behind bull.
My fav spell, discarding its effects, is Rusalka's Wrath. I love the way this mysterious girl comes from the deep o the ocean, with such timidity, but then she turns up her anger and pulls a wonderful lightning bolts, toasting the enemy.
Congratulations KI with such brilliant artwork, though it needed some changes in its effects, how come it might give a weakness? It's ridiculous.