The whole show, in some way or another, revolves around names of ghosts or spirits. The high school is called "Casper High," referring to Casper the Friendly Ghost. Also, the town Amity Park refers to the Amityville killings where ghosts reportedly caused a man to kill his family. Also, Danny's high school mascot is a raven, referring to Edgar Allan Poe's famous poem, 'The Raven.'
At one point, when Sam, Tucker, and Danny are at the entrance to the movie theater, there's a "Crash Nebula" arcade game in the background. Crash Nebula is one of Timmy Turner's favorite superheroes featured in Cosmo & Wanda - Wenn Elfen helfen (2001) another show created by Butch Hartman.
Another reference to ghosts being involved with the show is the main character Danny Fenton and his father, Jack Fenton. Danny and Jack were the father and son's name in Stephen King's Shining (1980).
In the original version, Danny and his friend Sam were supposed to have a telepathic connection.
Sam and Tucker would be in all but one episode of Danny Phantom.