MIPS the rabbit is found in the basement of Princess Peach's Castle when the player acquires fifteen Power Stars during the events of Super Mario 64. When Mario approaches MIPS, he runs away. After Mario catches MIPS, the rabbit gives him a Power Star. MIPS appears in the basement a second time after Mario has collected fifty Power Stars. Mario can catch MIPS again and will get another Power Star from him. After getting the last Power Star, MIPS will not reappear for the rest of the game.

In the remake Super Mario 64 DS, MIPS does not make a reappearance; instead being replaced by the rabbits scattered throughout the castle for each character to find. They're modeled after MIPS, but they do not give up Power Stars. Instead, they give up keys to unlock minigames in the Rec Room. Two of Mario's, one of Wario's, and one of Yoshi's rabbits can be found in the same location MIPS was in the original game.

Along with Mario, MIPS was the first character created for Super Mario 64. MIPS was used extensively in early Nintendo 64 test simulations and ultimately made it into the final game because the development team liked him so much.

MIPS also makes a cameo appearance in Mario Party 3 on the Woody Woods board where several can be seen around the board.

Encounter types in Pokémon Yellow are defined by a single byte, with all used types including standard wild Pokémon encounters, those that take place in the Safari Zone, and the encounter initiated during the Old Man's Pokémon-catching tutorial. Encounter type 03, however, goes unused. In this mode, attempting to fight, access the item menu, or switch Pokémon triggers the unique message "Hurry, get away!". The player thus has no choice but to run, though fortunately the chance of escaping from this encounter type is hardcoded to always be set to 100%.
Because this encounter type only exists in Yellow, it may be that players would once have had the option to obtain their own Pikachu beyond the walls of Pallet Town, rather than being forcibly gifted one by Professor Oak before leaving. In this scenario, an encounter mode in which players were forced to escape if their party was empty would be essential for preventing the player from sending out an invalid Pokémon.
To force this encounter type, input GameShark code 010359D0 and then trigger an encounter.

In addition to the unused trade from Red and Blue, Yellow went ahead and added two more unused in-game trades, possibly placeholder data related to the removal of the in-game trades in Cerulean City and Vermilion City. These two unused trades would allowed the player to trade a Pidgeot for Pidgeot and a Mew for a Mew, with both of the received Pokémon having the nickname まつみや (Matsumiya, presumably after Toshinobu Matsumiya, who is listed in the credits of Yellow under Game Scenario). The English localization keeps the unused trade data, but changes the names of the received Pokémon to "MARTY" and "BART", respectively.

Pokémon Yellow was programmed with a few special considerations to take Generation II's Time Capsule in account, which will translate a Pokémon's catch rate into a held item when transferred. As such, Dragonair and Dragonite's catch rates were lowered from 45 to 27 (Dragonair) and 9 (Dragonite), which makes them significantly harder to catch, though neither of the two Pokémon can actually be encountered in the wild in Red and Blue. In addition, this changes their held items from a Bitter Berry in Red/Blue to a Protein (Dragonair) and Antidote (Dragonite). While Dragonair can be found in the wild in the Safari Zone in Yellow, there is still no way to have a wild encounter with a Dragonite during normal gameplay, leaving its catch rate and subsequently its held item to go completely unused.