Umm... Yeah... This card sucks. There is only 1, count them: 1, situation where this card can be useful and it is the following:
You swing with a tramply creature whose power is several times more than your opponent's life total (for the sake of both argument and excess, let's pretend it's a Sutured Ghoul that you exiled 4 Jokulmorders for, making it a 48/48) and an Armor Thrull (because you run an awesome deck). Your opponent decides to block your giant Ghoul with a Sentinel and pays the 0 cost for his ability and blocks your Thrull with a Birds of Paradise (let's pretend your opponent got hit on the head recently and can't think straight). With this card, boom! Suddenly he takes 47 damage to the face while you only lose 2 life and all of your gribblies die.
However, there is one major flaw with this plan. If you use the above setup, your opponent could have lived if he didn't block your Thrull. You see, this card requires 2 blockers to work, so if your opponent only blocks 1 creature. this fails. It also fails if you're trying to swap a flying blocker that's in your Kulrath Knight's way with a ground-walker because it can't cause illegal blocks. Finally, it fails because it'll wipe out any gribblies you have and deal you 2 damage in order to make one switch (or, it can do that if your opponent uses Rishadan Port on it (sidenote: Look, an actual good use for Rishadan Port! Now to find someone dumb enough to use this card...)). All in all, it fails.
Pros: Switches blockers in very, very limited situations
Cons: Hurts you, hurts your creatures, and probably hurts your family somehow