The Dorm Mother's design is a monstrous version of Disney's Minnie Mouse, in her 1930s design.
Phantoma is visually based on the Phantom in Phantom of the Paradise (1974), itself based on the Phantom of the Opera (a disfigured being who wears a mask).
The headmaster is a Hell-version parody of Elvis Presley, therefore named Helvis. In Hell, Helvis lives in the Heartbreak Hotel. Presley released his song "Heartbreak Hotel" in 1956, and it eventually topped the Billboard Top 100 for seven weeks.