Mr. Do!'s Castle for the Atari 5200. Based on the Universal arcade game, Mr. Do!'s Castle is the sequel to Mr. Do!. As the little clown Mr. Do!, your job is to rid your castle of red, green, and blue unicorns that are roaming around the hallways and climbing up and down the ladders. If you get bitten by one of these pests, you lose a life.
Mr. Do!'s Castle is made up of eight non-scrolling scenes, and each scene is composed of seven floors. The middle five floors of each scene are made up primarily of blocks. Most of the floor blocks contain Mr. Do!'s favorite food, cherries. To eliminate a unicorn, you can knock out a block with your hammer while the unicorn is directly beneath the block, effectively crushing it to death. In levels one and two, you can whack a unicorn on the head while it is standing on a block.
To complete a scene, you must knock out all of the cherry blocks or kill all of the unicorns. Three of the blocks on each level contain keys. If you knock out all three key blocks and then go to the door on the seventh floor, the unicorns briefly turn into bonus letter unicorns that can be hit with the hammer for extra points. If you spell out the word EXTRA at any point during the game, you win an extra life.
This addition of Mr. Do!'s Castle is very similar to the ColecoVision game, but with one notable exception. In this version of the game, the red and green unicorns do not change colors if you hit them too many times with your hammer. However, in both games the blue unicorns can clone themselves.