An original Atari 2600 homebrew by Eric Ball.
From the instructions manual:
The objective of Skeleton+ is to eliminate Skeletons without being killed yourself. Use your Joystick Controller to maneuver your way through the maze. Press the red controller (Fire) button to shoot your Undead Disintegrator. When a Skeleton is destroyed, another will take its place. Destroy five Skeletons and you will enter the next maze. Complete all eight mazes to win your freedom. Being touched by or touching a Skeleton will reduce your life. When your life reaches zero, the game is over.
Each new Skeleton is stronger than the previous and will require more hits from your Undead Disintegrator to be destroyed. You are also not a dead shot with the Undead Disintegrator so sometimes a Skeleton will require more shots to be destroyed. Although each new Skeleton starts moving slowly, the speed with which the Skeleton moves will gradually increase until it is destroyed.