The Shop

Not to be confused with Toad's Shop from Mario's Adventure, though these 2 areas may be connected.

The Shop is an anomalous area and gameplay mechanic found in some personalized copies of Super Mario 64. It commonly appears in the Castle Grounds, Courtyard, other outside area of Princess Peach's Castle, or even a room inside the castle. If it appears outside, it typically appears as a wooden stand with several items on it being ran by a Toad, Bob-omb, or even Wario or some other character, or a small shack. As the name suggests, the Shop allows the player to buy items. Interestingly, the area is commonly reported to have the music of the shops from Legend of Zelda: Ocarina of Time, implying the music may have been recycled from this unused area.

General Description
The Shop generally brings up a new menu that allows the player to buy objects, alongside a counter of how many coins the player currently has and an animation of the shopkeeper character, who will occasionally have dialogue in some reports. The Shop will usually require the player to use coins the player has collected throughout levels, saving them instead of instantly getting rid of them like in the base game, allowing them to purchase items, though other reports claim it requires Power Stars or other anomalous collectibles.

The Shop most commonly sells extra Power Stars, though can also sell power-ups that will activate when the player next enters a level, and even keys to certain rooms, either new parts of the castle or already existing rooms that are now locked behind a key door. Other reports even say that the shop can unlock playable characters, levels, unlock caps without a Cap Switch or Cap Switch level, or even special moves like the unused Spin Jump or special Triple Jump typically unlocked from Yoshi.

The Warehouse & "Missions"
The Shop reportedly has special "missions" similar to a regular level alongside the sold Power Stars. The most common is the shopkeeper being robbed by thieves, usually being Koopas, Goombas, or some other group of enemies with unique coloring, that the player must find around the game, or in a unique area called the Warehouse that takes place in the Shop's storage room. This area is usually quite vast, with mazes between shelves and boxes, and large bottomless pits that can be navigated with large pillars of boxes and items. This area is commonly unlocked after the thief mission is completed, though could also be unlocked if the player finds a Warehouse Key somewhere in the game, potentially even being held by one of the thiefs. Upon clearing the Warehouse area and/or finding the thieves, the shopkeeper will typically reward you with Power Stars or some other unique collectible. The Warehouse has also been reported to be accessed without any of these requirements however, and has also been reported to be a full course at times. Other missions include finding specific objects for the shopkeeper to sell, getting a certain amount of a specific collectible, or doing special "challenges" in levels such as clearing a specific mission in a time limit or with only one health.