I'm actually surprised at how powerful this deck can be. I get boards equal or better than classic handbuff paladin, but with a much better early game.
This is basicly a zoo deck that suddenly has huge boards near the end.
Why is Hir'eek, the Bat suddenly good?
Because of redundancy. This isn't the only card in the deck that likes being buffed, so you don't have to wait to draw it to go off. Also, when you draw it later, you can count on drawing buff cards since there are so many now. And make no mistake, this card is REALLY good in the deck. Nearly always 7 4/4's. Often more.
Why is Spirit of the Bat suddenly good?
It still isn't!! I took it out.
Just try it out. It's a lot of fun!