Skullman is a reoccurring level creator and meme originating in the Super Maker Bros. series.
Skullman first appeared in the season 1 finale of Super Maker Bros. as the creator of SBB: ROTHBHidden Block Fun House. He submitted the level saying that if Jirard completed it, he would sign up for Game Wisp. According to the Mario Maker timer, Jirard beat it in 25 minutes 56 seconds (at the time, a new record). A skull was added to the thumbnail to make more work for the editors.
Skullman reappeared in season two of Super Maker Bros. The Beard Bros. spent just under 3 episodes completing his submission for the haunted house theme titled Skullys house of ghosts (v.SBB). Alex apparently has an obsession with him because he continues to mention him in nearly every episode thereafter.
Season Three Edit
Skullman re-appears in the newest reincarnation of the maker bros series, now including Brett Beyone. Sneaking his new small creation in under the guise of the first user-created theme for Jirard "Switch Factory #1" in Skullmans specialty game theme of Super Mario World. Taking roughly less than one episodes time to complete, the announcement of a week of Skullman made levels was made making him the new Beard Bros "Riddler-esque" Villain character in Beard Bros lore. In addition to the announcement, Ted in this episode delivers a message from Skullman to the Beard Bros describing how this level was made shorter for a theme video, or as Brett puts it "an appetizer".
According to Comments from that video, and some of the following episodes, Skullman seems to be in the works on creating his next devilish design for the Beard Bros.