Hidden: Source

Deep within a secret labratory he was known as Subject 617. Now that this invisible mutant is on the loose, they call him “The Hidden”. He’s armed with a knife, superhuman strength, and an unquenchable thirst for blood. The mercenaries of the IRIS squad have one mission: use teamwork and their high-tech weaponry to eliminate him — or die trying.
This unique action/horror HL2 multiplayer mod allows one invisible Hidden to face off against eight elite IRIS agents.
Get ready…the hunt is on!