Deep Blue

Deep Blue is a horizontally scrolling shoot 'em up set entirely underwater. You control the A.N.G.E.L. Fish Attack Sub, a fish-shaped submarine defending Earth from an alien invasion that has mutated marine life into hostile creatures. The game features four stages, each ending with a large boss such as a giant jellyfish or nautilus. Unlike traditional shmups where enemies fire bullets, most creatures attack simply by ramming into you with unpredictable movement patterns. You start with a weak Pulse Bullet and can collect power-ups for three weapons: Bubble Beam (laser stream), Swirl Cutter (powerful single shot), plus speed boosts and healing items. Each weapon can be upgraded three times, but taking damage reduces your weapon power by one level and removes your speed upgrade. Your submarine regenerates health slowly when not firing. Beating the final boss simply loops the game at higher difficulty with no ending.

PC Engine

Released in Japan on March 31, 1989, by Pack-In-Video, and in North America on February 15, 1990. The game is infamous among PC Engine shooters, often labeled as one of the worst on the system. Electronic Gaming Monthly gave it 15/40, and Famitsu scored 19/40. Critics point to sluggish movement, clunky controls, and the brutal punishment of losing power-ups on every hit. The small letterboxed screen, bland backgrounds, and irritating music further hurt the experience. Enemies swarm in large numbers, and the final stage features foreground pillars that obstruct your view. There are no continues unless you know a cheat code. The game can be completed in under 20 minutes, but most players will struggle due to unfair difficulty. Despite its flaws, the detailed fish sprites and unique underwater premise remain its only redeeming qualities.