Hydra
In Greek mythology a Hydra was a serpent-like water monster that had many heads, and had reptilian traits. Each time you cut off one of its heads it grew two more in it's place. It had a poisonous breath and its blood were very deadly. The Hydra of Lerna was killed by Heracles, and its lair was the lake of Lerna. Their was a passage in the sea to the Underworld. The Hydra was the guardian of the passage.