Ophiotaurus

The Ophiotaurus is an ancient monster that could bring down the gods if it was slain and its entrails were sacrificed. It was a half-cow half-serpent creature. Unlike most monsters, the ophiotaurus is actually very tame, sweet and innocent. Thanks to Poseidon, the Ophiotaurus is currently safe in an aquarium at Olympus.

Tips for demigods
If you see one report it to Olympus ASAP