Wario

Wario is a recurring character in the Mario spinoff series, first making his appearance in Super Mario Land 2. He is an exaggerated take on Mario, and acts as the plumber's rival in several sports games. After his appearance in Super Mario Land 2, he would go on to span several spin-off games of his own like Wario Land or the WarioWare games.

No developer has ever talked on Wario being set to appear in Super Mario 64. However, he seems to appear in several personalized copies of Super Mario 64. In the game's remake, Super Mario 64 DS, Wario is one of the four playable characters and the last to be unlocked.

Wario Apparition

 * Main page: Wario Apparition

The Wario Apparition is the large, disembodied head of Wario that appears in some personalized copies of Super Mario 64. He appears past the 30-star door in the castle's basement and will chase Mario down the endless hallway while clamping down his teeth. Although most people who experience the Wario Apparition are unable to recollect his behavior as they end up suffering from stroke-like symptoms when trying to.

The Wario Apparition has become one of the most popular Super Mario 64 conspiracies lately, becoming a widely circulated meme and joke amongst internet culture.

Wario Mechanic Tweaks
In Super Mario 64 DS, some say that their mechanics can be altered to be more useful of a character. For example, special items, commonly several-pound weights can spawn that only Wario can pick up that can destroy enemies, special bricks, or fill holes in the ground that couldn't be filled otherwise. They can also use the iconic Wario Land shoulder bash if you do the 3 punch/kick combo, allowing the player to charge through enemies and bricks. He also takes one less damage than normal due to his tanky design, and his ground pound releases a watered-down version of Bowser's shockwave that can deal damage to weak enemies and break nearby objects, but it pushes back any strong or flying enemy that isn't damaged otherwise, briefly stunning them. He can also reportedly use the Wild Swing-Ding from Multiplayer Mode in singleplayer in some reports, allowing him to knock out enemies, pick them up, swing them around and throw them, similarly to Bowser's boss fights.