MORBIUS

The Six Arms Saga begins with a cure that backfires: Peter Parker's homemade serum, meant to switch his spider powers off, amplifies them instead and leaves him with four extra arms. By The Amazing Spider-Man Vol. 1 #102 (1971), by Roy Thomas and Gil Kane, he is hiding the mutation in Dr. Curt Connors's Southampton lab when two emergencies collide — Connors relapses into the Lizard, and the newly debuted Morbius comes hunting for blood.

The clue arrives by accident. Morbius bites the Lizard mid-brawl, and Connors's mind surfaces inside the reptile body, scales and all — something in the bite pushed the transformation backwards. Connors deduces the mechanism: Morbius did not take something out, he left something in, an enzyme carried in the Living Vampire's blood. The two scientists — one six-armed, one intermittently a lizard — resolve to borrow some.

Getting it nearly kills everyone involved. Connors draws a sample, Morbius wakes, snatches it back and flees across the rooftops with Spider-Man webbed to his trail, until the vampire clips a bridge and drops into the river. Parker recovers the vial from the water and injects himself — and the four surplus arms melt away, his ordinary two-armed anatomy restored, while Connors likewise shakes off the Lizard. The monster of the story was also its medicine cabinet, and Morbius, who needed that enzyme to live, sank out of sight as the saga's unwilling pharmacist.