Hearthpwn

This is the deck I finally beat HC Baron Geddon with. Credit where it's due: it is based on Tehstool's deck. But the changes I made make it work for me, whereas his list didn't. 

The Clockwork Gnomes (in place of the usually dead or detrimental Wailing Souls) are very important not only because they give a you an extra 1-drop but because the Spare Parts can help round out your mana. The Cabal is for stealing those irritating Imp Gang Bosses and Flamewakers. Finally, Alex can be used either defensively or offensively. She's also a GREAT Recombobulator target, especially if she gets damaged in trading. 

Playing the deck: If you don't get a Gnome, Cleric or Mind Vision in your opening hand, concede and restart.

Much of the game will be spent fighting for board control, but whenever you have the chance to do some face damage, do it! 100 health is a lot.... Eventually, if you got lucky and things went well, you should have a decent board and now you race him before fatigue and/or his hero power kills you.

You'll usually need to heal every turn. It helps you use your mana, anyway .

Try to use your and pandas and Silences on lower value Living Bomb'ed minions and save your Recombobulators for 5+ minions.

Finally, make offerings to RNGesus for good Thoughtsteals.