I was anticipating this one, and I have to say that it is very overpowered. If the mounts were all released, this is the one that I would have in my deck
You know why? No creature save mutations has an ability to destroy or steal permanents. Butterfly Effect, however, allows you to destroy permanents - for 8
to cast, 3
to use, and 2 cards (a Butterfly Effect and a creature card that MUST have an attack of less than 3).
These are some huge payoffs for a simply creature with an expensive "Destroy" ability.
And here we have a creature that can not only destroy permanents for a cheap cost, but it can STEAL them. And it's a creature, which means you can spam as many of them as you want! And all you need is one of these cards!
Definitely overpowered. I'm not too sure how to balance it, besides replacing the ability altogether.