Hydra

The Hydra was a cut enemy from Half-Life 2, even though it was shown in the trailers. Originally it was supposed to be a large underground entity that had numerous tentacles that went up to the surface. These tentacles were neon blue, slightly transparent, and were capable of piercing itself through prey, such as a Combine Soldier in the trailer.

It was cut from Half-Life 2 due to difficulty in coding, hard to kill, less impressive when fighting Gordon then it was fighting NPCs, and its AI proved troublesome.

It is very similar to the Tentacle and may be related to it.