Emerging from the Jungle Planet (Animatron/Beast Planet) within the Unicron Trilogy, Undermine positioned himself centuries before the main conflict as an innocent, attacked traveler before a younger Scourge. This encounter, fueled by Undermine's mistreatment by unknown aggressors, swayed Scourge away from mentor Backstop's pacifism, igniting war against the planet's rulers and criminals. Undermine attached himself to the ascending warlord, becoming a bodyguard alongside Brimstone. As Scourge's primary enforcer, Undermine pacified the populace through espionage and assassination, directly opposing his brother Repugnus. He operated as a silent spy and hunter, tracking dissidents, extracting secrets, and eliminating targets. His reputation as one of the galaxy's most skilled hunters stemmed partly from no prey surviving an encounter. A crucial Cyber Key Code backstory revealed his betrayal of Scourge's prior bodyguard, Shrapnel; Undermine forged evidence of Shrapnel insulting Scourge's leadership, securing Shrapnel's dismissal and his own appointment. Undermine appeared in multiple episodes, often with Snarl and Brimstone. He guarded Scourge's temple, confronting intruders like Megatron and later Optimus Prime's Autobots. When Overhaul challenged for the Jungle Planet Cyber Planet Key, Scourge initially dismissed him but permitted Undermine to battle him upon Overhaul's rematch. Overhaul defeated Undermine, proving his worthiness to face Scourge again. Undermine fought Autobot forces, clashed with Snarl, and intercepted Backstop, consistently prioritizing Scourge's commands over pleas for aid, notably refusing Lori during Decepticon attacks. Catastrophe struck as Galvatron manipulated a black hole, dragging Jungle Planet through a Space Bridge. Forced into retreat, Undermine fell into a lava crevice but was rescued by Brimstone. After Scourge's incapacitation and subsequent clarity via Snarl, Undermine aligned with the Autobots against Galvatron. He evacuated the dying planet aboard the ancient starship Ogygia, joining the united Autobot assembly. In the final battles, he assisted in constructing rockets to reposition Jungle Planet and participated in the Space Bridge project under Metroplex alongside Brimstone, shifting from combat to construction. Undermine transforms into a robotic Spinosaurus with a sail resembling a fish's dorsal fin. His Jungle Planet Cyber Key gimmick, inserted into the sail in dino-mode, activates a spring-loaded blade extending from his head, functioning as a horn in robot mode. His detachable tail becomes a flail weapon in robot mode, attaching to sockets on his hand claws. Toy color variations exist: Hasbro used higher-contrast greens, while Takara favored vibrant light greens with pale camo-olive accents. This mold was repurposed for Cybertron Repugnus and later re-released under different branding. A distinct 2010 Transformers toyline version presents Undermine as a Decepticon of undetermined universal origin, characterized by chronic complaining about perceived shortcomings, fellow Decepticons, and circumstances. His negativity alienated other Decepticons, leading to avoidance that further fueled his grievances, including accusations of poor teamwork. This iteration reused the Cybertron Undermine toy mold.