As a Mage the best option for you is to use Transmogrification Curse with the option of following it up with an Incendiary Curse for a DoT on the opposing Hero. Warriors have access to Crippling...

Each class has there own way to deal with Fatties, so it will depend on what class and deck archetype you're playing. Let me know the answer to that and I will try and provide you with some more...