Hearthpwn

The deck I used to kill Baron Geddon in normal mode. Try to mulligan cards that fit your mana curve. You might take damage in the first turn if you have no 1 drop, but otherwise you should be able to use all your mana every turn. You should be able to kill him within the first 10 turns.

Cards you can sub/replace:

The Sludge Belcher and Savannah Highmane are useful and powerful cards, but I never used them against Geddon. You can sub for any same cost card.

The Freezing Trap is there to give durability to your Eaglehorn Bow and stall to get lethal. Most times it'll send back a low cost minion so you can sub it with another trap like Snake Trap. 

Hunter's Mark is for insurance against the Molten Giants he throws. You can sub it for something else.

You can also use this deck against Majordomo Executus. It runs the same way.