During preview season for Kaladesh, Todd Anderson posited a Mardu Reanimator deck built around Cathartic Reunion, Refurbish, and Gearhulks. He ended up abandoning the deck as not quite powerful enough to justify being so linear. That issue may seem insurmountable, since there really aren't more powerful artifacts to recur in Standard right now, but that's only one potential fix. The other is to make the deck less linear.
That's what this version of the deck attempts to do through the incorporation of the Haunted Dead / Prized Amalgam engine and some much-needed interaction. Lightning Axe and Fiery Temper fit the deck perfectly, and between Cathartic Reunion and Tormenting Voice, you should be able to find the removal you need to survive the early turns of the game.
Once you reach the mid-game, recurring a few Gearhulks should be easy. Combustible Gearhulk's trigger will often mill another target and you can dig for another reanimation spell. The issue comes in closing the game once you gain an edge. Eventually you will run out of gas or the battlefield will clog to the point where you can't finish your opponent off.
Key to the City is a heady addition that solves this exact problem while also being a discard outlet and card advantage engine. It means you don't have to worry much about Ishkanah, Grafwidow buying time for Emrakul, the Promised End to come down and ruin your day. This deck doesn't want to play a super-long game. You want to land a big threat or two early on and ride it or them to victory.
But not every game can go according to plan, so having options like grinding with Haunted Dead and Prized Amalgam or siding in a bunch of removal spells and playing a classic midrange strategy helps the deck overcome the limitations of its engine.
Again, these changes may not seem like much, but it doesn't take a lot to solidify the weaknesses of a linear deck provided the engine doesn't take up too much space in the deck. In this case, all the pieces are functional cards for a midrange deck in their own right and there is ample space to tweak the deck with the needed interaction. And you'll still get to annoy your friends with endless Hulk Smash! jokes, which is a big game.