Birthday Toad

The Birthday Toad is an anomalous, yet typically harmless NPC in Super Mario 64 located around Princess Peach's Castle, commonly replacing a random Toad within any floor, including ones locked behind personalization. The Toad's appearance is relatively similar from copy to copy, that being a Toad with either blue or rainbow spots and/or a small party hat placed upon its head.

Behavior
As mentioned earlier, the Birthday Toad randomly replaces any Toad on any floor, regardless of personalization, and also changes spots upon reloading the game. Upon interacting with it, a countdown that usually lasts for several days will begin, and the Toad will say "[x] days left." There doesn't appear to be a set limit for how long the Birthday Toad can be active, as some people have reported that their countdown lasts for about a year or longer. When the Birthday Toad's counter hits zero, instead of loading into the castle grounds when selecting a file, the player loads into a dark room. Inside this dark room seems to be a barely-illuminated Birthday Toad sitting at a table. Talking to him prompts him to say "Light it up." If the player is to turn around, they would see either a lighter or a candle depending on the copy. Bringing either object to the Birthday Toad will cause the candles of a birthday cake on the table to suddenly be lit up. Birthday music begins to play as the Birthday Toad speaks one last time:

"It's my birthday.

Thank You, Mario.

I'm so happy."

Upon closing the text box, a star will spawn. Grabbing it usually crashes the game, although some have reported that the star takes them to Delicious Cake.

Theorizing
Some believe that the Birthday Toad's purpose was to test the Internal Clock to see if it could keep track of dates. It may have been removed because waiting for days on end to get a star wasn't seen as fun to playtesters.