Selph (or Self) was a deleted Nightmaren boss from the original game, NiGHTS into Dreams[1]. It was intended to be in the game but was deleted from the roster at the last second because Yuji Naka believed the game was "perfect enough". Selph was supposed to be a concealed/secret boss. Yuji Naka said in his interview that Selph was based on the self archetype of Carl Jung's theory and described him as "Myself I could never be exceeded" [2], which probably meant that Self was also based on vanity/pride or ego. Self's appearance was unfinished prior his deletion.
Even through Selph was deleted, a hacker discovered some of the Selph's data in the roster, right before Wizeman's[3]. This jewel of information included a music track of what would have been Selph's battle theme, entitled "Know Thyself," which bears an interesting resemblance to "Dreams, Dreams," leading many fans to believe that Selph has a strong connection to NiGHTS. Furthermore, on the disc for Christmas NiGHTS into Dreams, the menu image for NiGHTS[4] notably has a slightly distinct design from the "real" NiGHTS, leading some to believe Selph may strongly resemble NiGHTS. However, no data exists relating to any physical designs for the deleted boss, leaving fans to speculate and invent possible designs for themselves.
Another nugget of information discovered were parts for a sort of "mirror staff" and additional information regarding the data[5], found by another hacker.
Trivia
- Selph was supposed to be based on the Self archetype, which is the most complex one, that was probably one of the reasons why Sonic Team didn't make him in time and he would have created a conflicted story, since he was a secret boss. Also, NiGHTS is based on the Shadow archetype that is opposite of the Self. Selph could have made NiGHTS Into Dreams... an unique example where the Shadow is a positive character and the Self negative one.