Aquanaut

In Aquanaut, the protagonist has to find and kill the leader of an alien race which wants to destroy Earth. This alien is smart and is not easy to find, but humanity managed to track him down to an underwater location in the Caribbean. The game is divided into three levels with distinctive different gameplay mechanics.

The first level is a traditional, horizontally scrolling shooter. The protagonist, equipped with diving gear, has to make his way to the alleged position of the alien ship. Enemies are mutated underwater animals which are shot with the harpoon. There are also friendly creatures like dolphins and mermaids (their kiss gives an extra life) and military crates which contain additional gear. Air is limited and has to be refilled at certain parts of the level.

In level two, the player has to investigate an underwater maze. He needs to find and grab various items which are used at another place to proceed. This section is puzzle-oriented and the action concentrates on obstacles which need to be avoided and single enemies.

Level three is also a maze in which objects need to be found (a decoder and keys) which need to be brought to a final location. However, it is set on land (Atlantis, to be exact) and therefore air is no longer an issue. The fights take a "run and gun" approach where the player shoots a lot of aliens and dodges their attacks. In this section the game flips the screen when another room is entered.