Hearthpwn

So, the goal here to control the board and dump tokens to absorb Omokk's hero power.  Anything that spawns another minions or brings one back when it dies really helps here.  

A fair amount of this boss's minions have 4 or less health.  So having swipes here can be really useful.  If you don't have legendaries here, I would say just add in more deathrattles and token generators(piloted sky golem, dragonling mechanic, and nerubian egg come to mind).

The cards to want to mulligan for are early game token generators, card draw, and some removal.  You'll want to save the naturalizes for the big threats like his 6/7 ogres or Mogor.   I would say the MVPs here are the savage roar and wispers.  As long as you can get enough creatures on the board savage roar does work.  And having a bunch of 1/1s makes his hero power fairly useless.  

Cenarius and tree of life are also really useful here, if you get bad draws they can help keep you in the game.   I would say you can maybe drop alextrasza, I didn't end up using her, but I could see a game where she helps;  Onyxxia might be a better fit for this matchup.  

TL;DR : Try to play on curve and survive, make lots of tokens, finish him off with tokens + savage roar combo.