Rockwell, the massive mutated mastermind behind the horrors of the Aberration, is the final boss of this DLC. He was the first ARK boss to trade total control over the arena with all movement, as he is rooted in a pool of Element for the entire fight. As such, he has access to area-denial attacks, projectiles that can faze through geometry, and a flood of Nameless and Reaper minions that spawn in later stages. He was also the first ARK boss to use non-traditional AI target selection methods since he could be completely surrounded by enemies and needed to attack multiple targets at once.

Rockwell surrounds himself with 8 tentacles, each capable of crushing any threats or electrifying sections of the surrounding arena. He is completely immune to all damage until all of his tentacles have been killed, which puts him into a temporary vulnerable state during which his chest splits open and reveals his heart. Once he gets up from this state, his tentacles all respawn and the cycle begins again.