The game was featured in The Humble Indie Bundle. Following the success of the promotion, Cryptic Sea pledged to go open source with the game which eventually happened on May 29, 2010. On 3 June 2010 Gish was ported to AmigaOS 4. A hack for the game was created soon after the open-sourcing that allowed Gish to grow larger and smaller.
Gish is a ball of tar who lives happily with his human girlfriend Brea, until one day a mysterious dark creature kidnaps her. Gish fights through several levels of enemies in the sewers of Dross until the final boss appears: Hera, Gish's former classmate who has an unrequited affection towards Gish. Gish rejects her, and Hera threatens to drop Brea into a pool of lava. After Gish defeats Hera, he must rescue Brea. If the player succeeds, Brea and Gish escape and become famous entomologists, as well as the world's first legal inter-species marriage. If the player fails, Brea burns to death in the lava pit and Gish goes on to live a life of celibacy, "volunteering most of his time to charity organizations that specialize in bringing lava awareness to the mainstream." In the latter case, Brea's picture is crossed out from the final group photo of the game.
In Gish, the player maneuvers the eponymous character, a 12-pound ball of tar. Besides movement Gish has four abilities: becoming sticky, slick, heavy, and jumping/expanding. When sticky he can climb up walls, stick to ceilings, and plant himself firmly to a solid object. Becoming slick makes Gish slippery and frictionless, letting him slide down pipes and squeeze out of being crushed. Using heavy turns Gish's body into a rigid weight, allowing him to fall faster, squash enemies, smash breakable platforms, sink in water, and resist being crushed. To jump, Gish must first compress his body, then expand to launch himself into the air.
Gish's abilities can be combined for use in certain situations - for instance, while both sticky and slick he can climb walls without grabbing loose objects, and while slick and heavy he can slide downhill at high speed.
All of the music and sound effects were created by Tim Smolens and Jeff Attridge of Game Audio Magic. The game features songs by Smolens' band Estradasphere, including Feed Your Mama's Meter from the album Buck Fever. Edmund McMillen frequently uses music by Estradasphere in flash games created for Diverge Creations.
In addition, Gish is an unlockable playable character in two of McMillen's flash games, Meat Boy and Spewer, as well as a boss, an enemy and an item in The Binding of Isaac. All games can be found on Newgrounds and have been remade for The Basement Collection, while Isaac is a separate game purchasable through Steam. Gish also appears in the Xbox Live Arcade version of Super Meat Boy as an unlockable character. He also makes an appearance in "Clubby the Seal", another game on Newgrounds.
In "Jelly Escape", a game on AddictingGames, he makes an appearance as an acquired skin.
The Gish will also be playable in the upcoming game UFHO2.