Half life: Decay

It also includes an expansion pack that is referred to as Half-Life: Decay, which was never officially available as an expansion for the Windows game until it was eventually recreated as a modification. The third expansion for the original game, it features two-player cooperative gameplay (in split-screen) with the two female scientists Gina Cross and Colette Green as the protagonists. It is meant to be played with two players at the same time as it is more puzzle-oriented than the original game and the first two expansions. Singleplayer is also possible, but then switching between the two characters is necessary to advance. When not active, the other character is AI controlled for basic actions