In Mermaid Madness the player takes the role of the weighty mermaid Myrtle who finally, after 112 years, found the man of her dreams: the diver Gordon. Unfortunately he is not very enthusiastic, flees into the water and jams himself under a ship. Myrtle's first priority is to save Gordon.

The player navigates Myrtle through an underwater labyrinth (although there a few screens above ground) and collects items. Those items have to be used in another location to proceed. It is also important to avoid enemies because touching them reduces her life energy, which can be refilled by finding beer bottles. There is no scrolling and Gordon's air supply acts as time limit.