In Multiplex, the player controls a small vessel or character that is made up of two pound signs (##). This vessel is sent around the board among a host of other enemy vessels, which can be a set of other characters (e.g. VV, **, ==, and so on). Each enemy vessel, when touched, activates it's self destruct sequence, giving the player a little time to flee the coming explosion. An explosion will trigger further explosions if other enemies or mines are nearby. Explosions will kill the character, destroy enemies, or removed obstacles.
The point of each level is to destroy all enemies, with each level growing in size and number of enemies.