Alan Gabriel: If you've lost the will to live, don't keep it a secret, I beg you, for I will grant you and your little android eternal peace!
The Hydra seems to be a creation of Eugene, formed from the remains of the "Wraithful Titan" (see episode three, "Electric City") salvaged by Rosewater's people. Like it's original, it's a giant electric eel creature, but is albino and has two additional heads with regenerative powers so that it can absorbed three-times the amount of electricity and three times the electric shock. It was invented to fulfill its "parent's" original purpose to provided the city with energy.
In Greek mythology, the Lernaean Hydra was an ancient serpent/water beast that possessed numerous heads.