When Mario and Luigi first visit the castle, the frames on the wall are empty. As levels are scanned through an e-Reader, those containing an e-Coin will have the coin's frame indented and its level number in the plaque below (the game's Wii U Virtual Console release has the frames marked from the outset since the e-Reader levels are built in). As such, the castle appears to be a sort of museum or trophy gallery.
The castle has three floors of eight frames each, with the second and third floors (2F and 3F) opening to Mario and Luigi once the player scans a level containing a 9th and 17th e-Coin. The player can teleport between floors by pressing and . However, despite the game containing the code and sprites to allow this, the e-Reader's failure saw only the completion of 1F (Super Leaf, Starman, Toad, Mario, Princess Peach, Luigi, Mushroom, Fire Flower), with American and Australian players able to collect only three e-Coins (Super Leaf, Starman, Mushroom).
Modifying the game's code to have 24 e-Coins collected, thereby filling all of the castle's frames, does nothing.
- The music played in the castle is very similar to the theme of Mushroom Kingdom in Super Mario RPG: Legend of the Seven Stars.
- Hodgson, David S J. Super Mario Advance 4: Super Mario Bros. 3 Prima's Official Strategy Guide. Page 113.