Gex is a side-scrolling platformer that follows the title character Gex, an anthropomorphic, television-obsessed gecko who must travel through the "media dimension" and defeat the game's antagonist, Rez. Gex must traverse through 24 levels contained in five different TV channels[3] which act as game worlds (accessed through a world map),[4] each filled with platforming stages and ending with a boss stage.[5] The goal of each stage is to explore and locate hidden television remotes which are used to unlock more levels. The original 3DO version of the game allows players to save their progress and resume from where they left off; all other versions use a password system. The player unlocks passwords or is granted a save opportunity by beating a boss stage or finding video tapes hidden in certain levels.[5] Every level contains a hidden portal which leads to a bonus level, the perfect completion of which earns the player a piece of the Planet X remote. Collecting every piece of this remote allows them to reach Planet X, an optional secret world.[6]
Many of Gex's default abilities take advantage of his special characteristics as a gecko.[1] In addition to being able to walk, run, and jump, he can attach himself to walls and ceilings and crawl along them using the suction pads on his feet, allowing him to reach higher areas.[7] Gex primarily attacks with his tail; he can whip it in a full circle to defeat enemies, activate switches, and deflect projectiles.[8] He can coil it into the shape of a spring to bounce off enemies and other objects.[9] Levels contain assorted collectible power-ups which can provide Gex with several different abilities, such as enhanced speed, invulnerability, and one of many different types of projectiles that can be launched from his mouth. Gex can obtain and utilize these power-ups by lashing his gecko tongue out and consuming them; alternatively, these items can be tail whipped in order to replenish lost health at the expense of the item's primary effect.[10] Gex's health is represented by three "hit paws", and he loses one whenever he is hit by an enemy or a hazard. If the player loses all of their hit paws, then they lose a life. The number of hit paws can be extended to six by finding a certain power-up.[11] The player begins the game with three lives, though more can be earned by collecting a hundred Golden flies in a level. Losing all lives causes the game to be over, forcing players to restart from the beginning (or from they last saved in the 3DO release).[11]