The User Characters Mystery was a mystery created by Cobweb as an April Fools joke where he created accounts for Fantendo's fanon characters on the Fantendo Forums. He created multiple accounts on the Fantendo Forums for user characters such as Litle P, 3.14, Smile (who he incorrectly named Ghost Smile to try and confuse people more) and a few more. McQueenMario also created The Return of: 4.13 user a large time afterwards.
3.14 was the first.
Litle P was the second.
Smile (formerly Ghost Smile) was the third to be created.
After COKEMAN11 stated that PalmMan was coming, PalmMan was created.
Other characters such as 4.13 and Sandslash P were created.