Oddly placed objects

Several objects in the Super Mario series appear to be placed oddly or accidentally. Many are in areas that would be unreachable in normal play. These are often normal objects that are simply placed outside of the accessible course geometry, and would function normally if interacted with through glitches or hacks.

The reasoning for the positioning of such objects varies. Some were probably placed by mistake. Others seem to be built over by course geometry changes that occurred later in development, and were never removed. Others still are unique entities altogether, and the reasons behind their placement are unknown.

Super Mario Sunshine
Several objects in Super Mario Sunshine are found outside of course bounds.

A well-known example is the secret book of Noki Bay, found in the mission Red Coins in a Bottle. It is placed inside a rock formation at the bottom of the titular bottle, behind a door that does not open. Reaching the book reveals that it has no collision and cannot be interacted with.

Another hidden object in Super Mario Sunshine is a Rocket Nozzle box, found inside the bell tower of Delfino Plaza. Players can reach this box and collect its Rocket Nozzle using glitches. When the Rocket Nozzle is not unlocked, it does not appear to cue F.L.U.D.D.'s standard message stating that it is a hologram.

Other misplaced objects include a Toad underneath Delfino Plaza, an extra tree inside a cliff face in episodes 7 and 8 of Bianco Hills, a banana bunch high above Pinna Park, and an invisible semisolid barrel in Ricco Harbor during the first Gooper Blooper boss battle.

Super Mario Galaxy
Toy Time Galaxy from Super Mario Galaxy includes a secret toy train. It is tucked below a blue checkered ramp on the first planetoid where Mario uses the Spring Mushroom. The toy is a miniature, unlike others in this galaxy, and has no known gameplay effect. Though most likely just a minor Easter egg, the specific intent behind this toy train's inclusion remains unknown.