It has shown to have multiple heads, with acid for saliva. It first attacked Hailey the moment she had managed to escape from Drake's machine, only to be punched in one of its heads by Hailey with a firey fist of hers.
However, before that, it was shown once before in New Divide as still being under construction.
It was encountered by James' team in New Peenemunde, deactivated and under the control of Soundwave. One of the major goals of that battle was to prevent Soundwave from reactivating the Hydra, which would have been undefeatable by the team in their state. The Hydra was destroyed when New Peenmunde was.