Served Plankton is a version of Plankton that appears in the lost episode creepypasta "Plankton Got Served", while his physical appearance in the mistful crimson morning mod is actually inspired by a deviantart drawing known as "Plenkton", created by the mysterious Moopintot. He is the opponent of the Freeplay song in Mistful Crimson Morning Called Served.

More facts here: https://fridaynightfunking.fandom.com/wiki/Mistful_Crimson_Morning#undefined