Moonlight Mansion is a towering, purple mansion located in an area in the Mirror World that was apparently abandoned sometime ago and made the stronghold for the Mirror World's Golems. The level is seemingly engulfed by nighttime at all times. This is the first level with a boss that gives a Mirror Shard. Its overall layout is rather big yet easy to navigate. High atop the mansion's spire is the Warp Star that leads directly to Candy Constellation, and down below is an underground laboratory.
Built into the ivy-covered castle walls are stained glass windows. These are most noticeable in the sanctuary where the boss of the level, King Golem, is fought. These windows display pictures of Gobbler, Wiz, Kracko, Mega Titan, and King Golem himself.
Moonlight Mansion is a spooky mansion under perpetual moonlight next to Rainbow Route. Its dilapidated outside is home to overgrowing vines, but its inside is well-lit and well-kept with shelves full of books and corridors equally full of enemies.
Both Carrot Castle and Moonlight Mansion share the same musical theme.