That card is very cool. It toys with mulligan strategy in a big way, because there's a reason to have this card in your hand apart from wanting to play it, which is different than every other card in the game. It's also a card that can only be done on a computer, yet isn't gimmicky at all, and that's exciting.
As far as strength goes, it's hard to say. At 5 mana and with no immediate board impact, it's slow in a class that already suffers from speed issues. For straight value, you're okay if this comes out as at least 4/7 (3 minions died). At 6/7 (5 minions died), it's a Boulderfist Ogre for a 1 mana discount, which is nice but maybe still not so exciting in constructed, where Ogre is not played except in budget decks. The best use in constructed might be a deck designed to pump this up to huge values as a potential win condition. I can't imagine that working very often though, since BGH and silence both handle it nicely.