Mar 6, 2016 ˇ Arena 3 takes 800 trophies to unlock. Once you do, these units are unlocked: Cannon, Barbarians, Rocket, Barbarian Hut, Rage, and X-Bow.
The combo can only be executed after you have placed down two or more spawns. In this video, I placed the Barbarian Hut, Tombstone, and Goblin Hut in the arena ...