Super Not-Cosmo is the alter-ego of Cosmo that he took up when he was accidentally discovered by humans.
Super Not-Cosmo is the name that the people of Dimmsdale gave Cosmo when he was seen saving Poof using his magical abilities. When they asked Cosmo who he was, he responded "Not Cosmo", causing Chet Ubetcha and the other people of Dimmsdale to believe that to be his real superhero name, Super Not-Cosmo.
Cosmo's costume was put together while he plummeted between two tall buildings and hit various clothing lines, causing him to appear in blue pajamas, underwear, and a red cape.
Trying to help Wanda, Cosmo stops by changing Poof's diaper for a wolverine and an electric walrus, and then, accidentally destroying the Turner's House. So Wanda threw him out of there, and he got mad about it and went to Dimmsdale Park with Poof.
There he accidentally materializes a whale to play seesaw with Poof, causing him to fly away, because of the whale's weight.
Cosmo then flies to save his son, and passing through a clothesline, pajamas and over that, underpants, end up on his body. Cosmo then got Poof before he hits the floor, saving him, but Chet Ubetcha was watching it all. So he asked Cosmo's name, that, to don't reveal the fairies existence, couldn't think of anything smarter to answer than "I'm not Cosmo".
So Chet Ubetcha started calling him Super Not-Cosmo, creating the alter-ego. He also has a hide-out directly inside Timmy's bathroom which he calls The Super Not Cosmo Secret Lair. He also has a butler, Wolfy, the wolverine, who according to Cosmo, eats him in his sleep. Cosmo also has an enemy named the Muffin Man.
Super Not-Cosmo's Secret Lair is the secret hideout of Super Not-Cosmo, located inside Timmy's bathroom. It is similar to the Bat Cave, Batman's secret hideout. It is quite dark and features a large computer that tracks criminals at large and a T-rex bone statue. The people who resided here were Cosmo, and Wolfy.