If the Player backtracks at a certain point in level 4-3, The Amiss Abyss level, and waits a while they can see a one of the eponymous creatures of the Metroid Franchise floating in the background in silhouette.

This is true in both the Wii U and Nintendo Switch versions of the game

The game is called "Holy Magic Century" in Europe and "Eltale Monsters" in Japan.

In 2018, former game director for Star Wars: The Old Republic, James Ohlen, said in an interview with GameInformer that he regretted having not pushed it to be "Knights of The Republic online" as opposed to making it traditional in the style of World of Warcraft, referring to it as "Star Wars World of Warcraft."

In an early announcement trailer for the Nintendo Gamecube, Animal Crossing was called (or at least promoted as) "Animal Forest for Nintendo Gamecube", outright referencing the original Japanese title of the game (Dōbutsu no Mori or "Animal Forest" in English). This suggests that either the English localizers were thinking of keeping the game's original title, albeit translated, or the title "Animal Crossing" was not yet finalized.

As of the 4.0.0 Update, which originally brought USB headphone support to the Switch, it was discovered that, via the use of the Wii U's Gamecube Controller Adapter, that almost every Switch game can be played with a Gamecube Controller. However, since the Gamecube Controller lacks a left Z-button the player does not have access to all of the controls of games that normally would utilize the Switch's ZL button.

A PlayStation release was planned and almost finished, however the game was cancelled because it didn't meet EA's standards.

According to Chris Glass, a member of the game's development team, the texture used for the bark on tree trunks is simply a green-tinted photograph of feces.

Bubble Bass has unused eye textures in the GameCube, PlayStation 2, and Xbox version's files, suggesting he may have been planned to have a larger role in the game.

The "Under Siege" musical theme appears to be based on part of Gustav Holst's "Mars, the Bringer of War" suite from Opus no. 32 "The Planets", this is appropriate due to the heavy war theme of the game and the situation the characters are in when the theme plays.

On the NES verion's System Construction Figure menu, inserting certain inputs will cause the cursor woman to remove her clothing. The final input freezes the game and replaces the woman with a hexagram.

The Arcana Edition of the game, which will be released for the Nintendo Switch and PlayStation 4 exclusively in Japan, comes packaged with exchangeable sleeves and a set of tarot cards featuring various fighters from the series.

If you enter "REFLOG" as a player name in the Genesis version, you will be brought to a secret golf mini-game.

Unused text in the GBA version's files suggest that all of the in-game spells (except for Expelliarmus) were planned to be upgradeable.

Fully modeled, unused traffic cars can be found in the game's data. They include an ambulance, a camper, and two trucks (one with a truck hauling pipes, and a tanker truck).

The Wart Boss Fight was originally going to sport tomato projectiles like its original incarnation in Super Mario Bros 2 featured. They were replaced with cabbages in the final release, but the tomato sprite is still present in the game, albeit unused.

The Gamecube version's code has unused text lyrics from Bob Gibson's song "To Morrow."

The texts states:

"If you had gone to Morrow yesterday, now don't you see
You could have gone to Morrow and returned today at three!"

The Korok seeds Link finds are actually Korok excrement.

Early music icons for the SpongeBob SquarePants DLC can be found in the PlayStation 3 version's data. They do not feature any LittleBigPlanet characters.

Entering the Konami Code on the title screen will change the game's logo from "Super Monkey Ball Jr." to the message "Super Nice Try".

The Xbox 360 version has text stating "PS3 Online Data Incorrect,". This suggests that a PlayStation 3 release may have been planned at one point during development.