Half-Life Wiki
Half-Life Wiki
This game is playable on PlayStation 2.   This subject is from the Black Mesa Incident era.This subject is in the Real world.
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Half-Life: Decay is an add-on included in the PlayStation 2 port of the first-person shooter game Half-Life, developed by Gearbox Software and published in 2001.

Like Gearbox's other expansion packs Opposing Force and Blue Shift, Decay returns to the setting and timeline of the original story, but with different player characters: two female colleagues of Gordon Freeman, named Gina Cross and Colette Green. Dr. Cross is the model for the Hazard Course hologram and can be seen at a point in Blue Shift. Dr. Green is a new character invented for Decay.

Although Gearbox completed a PC port of the game, Decay was never released on it "due to powers beyond [Gearbox's] control."[1] Decay is also not available through Valve's Steam service.


See also: Gearbox Software#Canonicity of the Half-Life expansions




The weapons available in the game are the Crowbar, Beretta 92FS, Colt Python, M4, SPAS-12, RPG, Mk 2 Grenades, and Snarks. Additionally, in "Xen Attacks", the player gets the opportunity to play as a pair of Vortigaunt Slaves, thereby giving them the ability to fire energy bolts and hit other NPCs with their claws.

Note that Satchel Charges and Laser Tripmines are also seen in the game, but they are not obtainable by the player.


Decay menu

The game's main menu.

Decay fighting Vortigaunts

Dr. Cross and Dr. Green fighting a Vortigaunt.

Unlike the other narrative-based Half-Life games, which are single player only, Decay is designed for co-operative play. While it can be played by one person, swapping between the roles of Dr. Cross and Dr. Green, the game is intended to be played by two players in split-screen. Various puzzles and combat situations throughout the game require the co-operation of the two characters.

The game is also unique in the context of the Half-Life series by being the only game divided into separate missions, instead of a single unbroken narrative.

Decay has a ranking system for all of its nine missions, ranging from F (worst) to A (best), based on accuracy, number of enemies killed, and damage taken. If all nine missions are achieved with an A level, a bonus mission, Xen Attacks, can be played as a pair of Vortigaunts, R-4913 and X-8973.


  • Even though this is another Gearbox creation, none of the new weapons featured in Opposing Force are in the original release of Decay.
  • This is the only Half-Life game to not have an official PC release.
    • A unofficial PC port of Decay was released on September 23, 2008, developed and released by independent Ukrainian developers with the help of other European developers.[2]
    • A third-party remake of Decay for Source, initially called Anomalous Materials but later renamed to Hazard Team, was under development, but has been cancelled.[3] As of 2018, another development group known as PSR Digital (the same one that made Black Mesa: Hazard Course) is currenly developing a source engine re-imagining of Decay called "Peer Review".
  • There is a way to cause a Resonance Cascade without actually sending a sample to Anti-mass spectrometer – by fiddling with specimen cart near its elevator.


  1. "Gearbox note on Decay". Retrieved 09 June 2006.
  2. Decay project status Retrieved 08 December 2011.
  3. Hazard Team on ModDB