G.I. Joe: A Real American Hero (1983)

S02E28 Sins of Our Fathers

Cobra Commander attempts to establish contact with the mysterious entity lurking in the pit beneath Destro's Scottish ancestral estate, but his efforts prove fruitless. Meanwhile, Dial Tone is honorably discharged from the Joes and quickly lands a job on a classified communications initiative—which turns out to be the very project aimed at reaching the creature. Flint is dispatched undercover to monitor Dial Tone's progress. When the machine finally powers up, Cobra Commander seizes the moment, commanding the entity to eliminate Serpentor.