Seems like a pretty handy idea. But it seems too situational for my liking. I can see it being a dead card in a lot of situations, such as a life rush, devourer decks, aether decks, all of which are quite common. It slows down fire rushes using lava golem/destroyer, but they tend to carry a lot of deflags.
A poison deck could be slowed considerably, but not if they are using puffer fish.
Still, it's a pretty neat idea.