On an evoker mage with the -1 cast speed Titan's Breath is ridiculously OP.  You can get your fail chance down to 3% for everything, and with instant cast time you can just spam it to permanently disable every enemy that isn't outright immune.  Combine it with something with the maul ability and you can then one-shot anything you knock down as well, even if you only hit for 1 damage.  Not only is it OP but time consuming as well, I've literally cast titans breath, attacked something with ludicrous armor and 200+ HP with my cave bear doing 1 damage, set speed to 5x and gone to the bathroom and come back before the damn thing finished.

Best way to nerf it would be to add a cooldown.  3 rounds would be enough to prevent it from being spammed.  Adding something to break the maul-knockdown synergy like an absolute cap (7 to 10) on the number of hits would also be a good idea.