Hearthpwn

Bomb Bomb Bomb and your dead... 

This doesn't seems like deck that can reach legend. Does 2x explosive traps and 2x unleash the hounds enough as AOE?

Where's the Screenshot that you reached legend with this deck? 

Tracking seems like a risky card to run here. If you hit multiple of your combo cards (Mecha'thun and Goblin Prank or Oblivitron, you instantly lose the game. Maybe Master's Call is better.

Also the deck might improve a lot if you could play and kill Oblivitron, summon Mecha'thun and play Goblin Prank on the same turn. If a minion already died this turn you can do it with Wing Blast, but it's not very reliable.

I disagree with the Master's Call because you have the Ursatrons which guarantee you to draw the Mecha'thun and Oblivitron. Tracking is just used to empty your deck faster, although you may have to take the risk and play it when you don't have all the combo cards in your hand :D

How does the combo work? Do you play oblivitron and goblin prank or let oblivitron summon mechathun, then goblin prank?

I haven't played, but it doesn't makes sense to play oblivitron and goblin prank because when oblivitron triggers the deathrattle, mecha'thun is still on the battlefield so the combo wouldn't work. Goblin prank has to be played on the mecha'thun summoned by oblivitron

Just posted a guide for those who are wondering how the combo works :)