Hearthpwn

This is the deck I used to beat Omnotron on Heroic. The idea is to take advantage of arcanotron for the first two turns with Explosive Trap and Arcane Shot. Mulligan for an explosive trap as it might be too late if you fish for it by trading with a mad scientist. Ideally, your explosive trap deals a 4-damage board clear, taking away Arcane Golems and/or Iron Senseis he put down with Recharge combos. After the board clear, rush face with your weapons and hero power. Knife Juggler and Freezing Trap maintain control of the board while you go for face. Knife Juggler acts sort of as a taunt as he will trade into it. AI will also probably help you along once he gets magmatron on board as he'll play cards inefficiently and bleed 2 life for each one. 

Originally, this deck also had 2 Cobra Shots in place of 1 hunter's mark and 1 unleash. I wanted to take advantage of arcanotron and electron but arcanotron either dies to toxitron or he uses it to trade. You could consider using cobra shots anyway if you play him and keep missing a last push for damage. Electron will likely be on the board to keep cobra shot cheap and playable. 

Some other card choices:

BGH - For getting past Magmaw, for a mech that iron sensei buffed too much or if you've got lethal but magmatron would drain too much health.

MCT - Past the explosive trap board clear, can snatch a minion from his board that gives you an extra turn to go face.

Cult Master, Savannah Highmane - AI seems to consider these high value targets that he will trade into. Savannah Highmane is Earth Shock bait that he will usually play while Magmatron is on board. That's two life gone and he'll trade into it, extending your face hunting. If they don't seem to work, you can switch them out for more aggro cards like Wolfrider and Arcane Golem.

Haunted Creeper - cheap beast you can play early or one you can keep for kill command lethals.