Abadox: The Deadly Inner War(1988)

Abadox is a video game for the NES, subtitled The Deadly Inner War. It is a side-scrolling shoot 'em up in the vein of Gradius and R-Type. The game is notable for its unique visual design, as the game takes place inside the intestinal tract of a giant alien organism. Abadox is also known to be difficult, since it takes one hit from an enemy projectile to be killed. In Abadox, if a player is killed, one must restart from a checkpoint passed before death.