On one of the last challenges (the one where you start with Index) there's a bug. Any of the spells that allow you to target players or creatures, it'll ask you which you want to target (creatures or players) but then if you choose Players it deals the damage to you directly instead of letting you choose yourself or the enemy.
I'm thinking they want you to solve the challenge without using the direct-damage spells on the opponent but they never explain this and it seems like a pretty sloppy way of going about it.