Slenderman is a character who first appeared in My Best Friend Slenderman. He also appears in the opening video that automatically starts playing of oneself when you visit Supermarioglitchy4's channel.
On a dark night, Toad wants Mario to go to the shop. When coming to the gray, dark scission Mario passed in previous bloopers, Mario could either go via Gay Castle or a forest. Mario chose the forest. On a glade, Mario hears sinister sounds and a ghastly voice. He then spots Slenderman, unaware of who he is, and takes him to the castle. Everyone but Starman3 runs away from Mario. Starman tells Mario who Slenderman is but Mario doesn't belive him. When searching for a job for Slenderman in the borough, Starman3 and some constables appear. Starman3 declares Slenderman (or "Slendy", which is how Mario cals him) under arrest. Though, Slenderman uses the Slender-Copter, but crashes with Mario on Wario's parents as Starman3 watches from the high building Mario and Slender Man are. Later, in the castle, Mario flushes Slenderman trough the lavatory after the latter starved.
- The forest where Mario meets Slenderman is actually from Slender: The Eight Pages.
- The ghastly voice and sinister sounds Mario hears are also heard in Slender: The Eight Pages.