The Game: As cuddly clown Mr. Do, you’re scrambling to squish all the unicorns who are invading your castle. You can repel them momentarily with your clown hammer, but you can only squish them permanently by knocking a brick out from the floor above. Most bricks contain cherries, but some also contain keys that unlock the door at the top. When that door is completely unlocked, touching it will transform the unicorns into walking plus signs; if you hammer five of them and spell the word EXTRA, you get an extra “life.” Clearing the screen of monsters or cherries advances you to the next level. (Parker Brothers., 1983)
Memories: I loved Mr. Do’s Castle in the arcade, and at the time I loved it on the VCS as well, though with the benefit of hindsight, I don’t think the home version was as definitive as I once thought it was.
The unicorns in this version of the game flicker maddeningly, about as bad as the ghosts in 2600 Pac-Man do, which is not a good thing. And whereas the arcade game’s archways would give you a chance to see if any unicorns were climbing down ladders toward you, in this game you can literally jump right up their butts and not even know they’re there.
Mr. Do’s Castle is a highly-prized collector’s item because of its unusual rarity. As the crash laid waste to the video game industry, Parker Brothers sought solid distribution channels to make sure their games made it onto store shelves, and wound up signing a 
deal with Sears that, while it wasn’t an exclusive deal, did divert most of the latter-day Parker Brothers games like Mr. Do’s Castle and Q*Bert’s Qubes to Sears stores. This game is incredibly hard to find on any platform.