This is an efficient card when it works but it doesn't always do something in every situation. The problem with this card is it requires a minion in play (outside of something like Tower Defense or Sinister Six) or it just doesn't do anything. It also makes your turn awkward since you wouldn't want to remove minions in play during your turn or you wouldn't be able to play this but you're not guaranteed to draw it so you're stuck in this dealing some damage to minions without killing it situation. Then if you don't draw it, the minion also gets to activate. Saving this card to use on the next turn also sucks since you're down a card for that turn.

When it does work though, this is great since it will still trigger a defense for things like Unflappable/Hard to Ignore/Electrostatic Armor/etc and guarantee taking no damage. But I don't think the upside is worth the effort.