Casey Kasem, who used to play the original Shaggy, and this incarnation of Shaggy's father, is a strict vegan and had suggested Shaggy should be a vegetarian as well. In this episode, however, when this version of Shaggy is forced to eat vegan, he doesn't like it at all.
The name Howard E. Roberts is a play on the American pulp fiction writer Robert E. Howard, most famously known for creating Conan the Barbarian.
This episode is full of references to H.P. Lovecraft a horror writer (famous for this type of monster) and his works, namely "The Call of Cthulhu":
The name "H.P. Hatecraft" is a play on the name H.P. Lovecraft.
Char Gar Gothakon himself bears a strong resemblance to Lovecraft's most well-known creation: Cthulhu.
The episode title may be a reference to In the Mouth of Madness, a film in which Lovecraftian horrors come to life out of books.
Ben runs with the gang to the rescue of Professor Hatecraft, but later on, he disappears.
All the gang members are dropped off at Darrow College by their parents, so, logically, the Mystery Machine should have been left at Crystal Cove. However, after solving the mystery, the gang approaches the Mystery Machine in the college parking lot.