Cards like Kobold Librarian , Loot Hoarder and Bloodmage Thalnos are excellent to keep against less aggressive decks to start rotating early on through your deck. Doomsayer is again a good pickup early on to try and maintain good board control to get to to the later stages of the game.
The aim of this deck is to stay alive until late in the game to pull off the Mecha'thun combo and kill your opponent.
The combo itself is quite straightforward. The setup involves playing Hemet, Jungle Hunter to destroy the majority of your deck once all the combo pieces are in your hand. Then you must play two Galvanizer to reduce the cost of your Mecha'thun to eight mana. Next turn you play Mecha'thun followed by Bloodbloom, which allows you to play Cataclysm and hopefully winning you the game.