Of inordinate size, the Hydra ("water serpent" in ancient Greek) is a creature reputed to be immortal, guardian of the Underworld. Its main head, here hidden in Mark Conlan's reinterpretation of the myth, was made of solid gold. The 8 others had the gift of growing back when cut.
Killing the Hydra is the second of the Twelve Labors of Hercules. How do you think he did it?