Castles are mainly the same as towers, however Bowser Jr. uses his "Friends" that fight Mario.
- Instead of going up, they go to the right like normal levels.
- There is a enemy in the World 3 Castle called a Whomp that can only be damaged with Ground Pound attacks when they are laying down.
- Sometimes there are scenes when Mario defeats a boss showing Bowser Jr. next to Princess Peach. When he sees Mario he gets surprised and yells at him and runs off to the next world.
- Half of the World 2 Castle takes place outdoors.