I was playing the current Tavern Brawl with a Druid Hero Power deck, and got matched against a Mage Hero Power. Got my Hero Power fully upgraded with 2 Groovy Cats and 2 Free Spirits, and had like 7 armor at the start of my turn.
Now we get into the weird part, the turn goes as follows:
1.- I draw a Crypt Keeper, so I use my Hero Power to make the cost go down to zero.
2.- I play the Crypt Keeper.
3.- I play a Reckless Apprentice that was in the Mage’s deck.
4.- Suddenly my attack goes up to 30, and I proceed to one-shot my opponent.
Really amusing when you are not in the receiving end.