Hydra

The Hydra as seen in the early development of Half-Life 2

The Hydra is a blue, gelatinous snake-like creature seen in the Half-Life 2 E3 2003 videos, intended for inclusion in the final version of the game. Despite positive reactions from both press and fans of the brief section it appeared in, the Hydra was cut from the game and has yet to reappear in subsequent titles.

The Hydra appeared at the close of a section of the presentation named 'Tunnels', which is easily recognizable as a work-in-progress version of the initial, warehouse based section of the retail chapter Follow Freeman. Whether the Hydra was in fact intended to appear at this stage of the game is unclear (the architectural transition from the tunnels as we know them to the Hydra area seems abrubt, suggesting that the area may have been uprooted from elsewhere and appended to the end of the section). The Encounter, like much of that shown in the E3 2003 videos was of a scripted event, and tellingly ends before the player engaged the creature in combat. This, as Ken Birdwell points out in Raising the Bar is the root of the Hydra's problems: "It was amazingly cool to watch if fight other characters, but it was zero fun to play against in first-person [...] You'd just see this non-descript blob doing something vague, then you'd be dead."

The loss of the Hydra was a significant part of early criticism of the misleading nature of the E3 2003 media, but bitterness towards the cut has since become less vocalized, and the hydra has instead become a symbol of Valve's readiness to bin great ideas simply because they aren't excellent ideas.

The Hydra is not officially considered part of the Half-Life canon, though its existence would not create any kind of contradiction in the game-world. Ken Birdwell, (Raising the Bar) mentioned how '[He'd] still like to see this in the the Half-Life Universe somewhere, maybe rethink its AI more along the lines of an Antlion.'