well with the "dark" white wizard (not a clue what to call him/her) you can make it where she has alot of offensive spells like harm for example. Maybe give her divine enhancement spells for weapons and evasion, etc. You could make spells that inflict divine damage (caus in rpg worlds, there are evil gods). If he's gonna make a "dark world" all he needs to do is pick up a Dungeons and Dragons player handbook to get ideas about making an evil cleric.

when i was making my own rpg after the ff3j project started to disband, thats what i did, because in my game you played as the evil characters. i wanted to make that, because you never see that that much in rpgs.