Cyren is a robot who uses a signal to control other robots and turn them against their "fleshy masters". His device even affects Serling, though Cody Jones is able to create a signal filter that enables Serling to accompany the Turtles.
With Serling's help, the Turtles track Cyren to a TV studio. Cyren sets a group of robots on the Turtles and then urges Serling to join him. Serling pretends to have fallen under Cyren's spell in order to get close to him, and then knocks him off the scaffolding he's standing on, which also breaks the remote the robot's been using to control other robots.