Goomboss

Goomboss (Originally named the Goomba King) is a boss in Super Mario 64 DS. They are a large Goomba with a mustache, eyebrows, red and white clothing and a crown. They are found in the Goomboss Battle level and unlock Mario when defeated. They first appeared in the original Paper Mario, being one of few characters to appear in a spin-off before a mainline Mario game.

They are mainly fought with Yoshi. They run around their circular arena with an army of Goombas following after them and do damage upon contact. To defeat Goomboss, the player has to throw eggs at them 3 times. The eggs can be acquired from the Goombas that follow Goomboss around. Each time Goomboss is hit, they grow bigger, gradually turn red and run faster. When defeated, they explode into a mass of Goombas and drop Mario's key.

Super Mario 64 Manifestation
Goomboss, along with Goomboss Battle, has been reported to appear in some personalized copies of Super Mario 64. They usually function the same, though they usually need to be punched or jumped on instead of being hit with eggs due to most personalized copies only having a playable Mario. When defeated, they usually drop a star, or a key unlocking a floor of the castle.

Halved Key
In some personalized copies, Goomboss only drops half of Mario's key. The other half must be obtained in Bowser in the Dark World, forcing the player to use Yoshi to fight Bowser. This usually does not happen in game. Why exactly this anomaly occurs is unknown, but it might have been to give the game more variety in it's progression, similarly to how you first have to catch a rabbit to enter the castle instead of being able to immediately enter the game like in the original Super Mario 64.

Red & Blue Goomba
Some have reported that Red Goomba & Blue Goomba from Paper Mario 64, Goomboss' closest minions, can appear in the Goomboss boss fight. They typically replace the Goombas that follow him, and have the same behavior. However, some have claimed they have to be defeated before the regular Goombas spawn to progress the fight, requiring you to jump on them 2-3 times. This is reminiscent of the Enemy Discoloring phenomena in the original game. These Goombas can also reportedly appear in Goomboss Battle as minibosses, having to be defeated to progress, either due to blocking platforms or dropping keys to the pipe that leads to Goomboss.