Description An all-against-one multiplayer mod for Half-Life 2 in which one player is invisible, equipped only with a knife and grenades, and everyone else is a gun-toting marine charged with hunting him down. Being a marine is conducive to wildly twitchy paranoia, while being the Hidden is mischievous joy. The first official release of the Hidden: Source, A Half Life 2 Modification. In this multi-player mod, you play as either an I.R.I.S Mercinary, or the secretive Experiment 617. In the game there is only one player as 617, the other players are the mercinaries, it is their job to work together to kill 617. But there is a catch, 617 is invisible and armed with a knife. 617 must use stealth and agility to outsmart the mercenaries and pick them off one by one.