Hearthstone: how can you have a minion with 320 attack points!?!?!?

I was playing with Hearthstone, while a guy made a couple of combos... doubling the health of a legendary minion... switching it with the attack points... making them equal... and so on and so forth. Long story short, he made his minion to achieve 320 attack points!!! I was so lucky to have a "Mind Control" card and enough mana to steal it before he used it! And BAM!!! 320 POINTS TO YOUR FACE :D