Aang is going to use the mask to help himself survive the fire and floods, and it's going to make him go full Rabidtar on everyone. This means lots of property damage, fancy bending, scary glowy children, and death.

If Aang's not bought out, I'm going to have the mask kill him after his rampage runs its course. He will be horrified when it's all over and everyone who's killed will get a personal apology. Who wants him?