Some of the "maniac" characters are credited as two different performers. The film production shut down for three months due to financial difficulties. When shooting resumed, many of the performers were unavailable and were recast as such.
This is, for all practical purposes, is an unfinished film. Severe budget and production problems brought filming to a halt multiple times, at one point for such a long period that much of the cast playing the maniacs had to be replaced due to most of them not returning because of other obligations. Also, a lot of the script had to be cut or altered to save money, and the originally intended final battle between the protagonists and the maniacs was never filmed, thus leaving the film with its rather abrupt and inconclusive ending. It is also suspected that better explanations of the maniacs, their motivations and their origins was in the original script, but never filmed due to production problems. No copies of this script have been found, and the cast and crew either don't know or remember what the creature's background was intended to be, don't want to talk about it due to bitter feelings over the production, or have since passed away.
Though it's never discussed in the film, according to the script, the Maniacs are from another dimension and they come to Earth via a portal that's in the back of an old truck inside a storage facility at the foot of the Golden Gate Bridge in San Francisco.
Initially there were upwards of 27 Maniacs penned into Mark Carducci's script, but for budgetary reasons the gang of other dimensional monsters was whittled down to 12 who go by the names Axe, Ape, Mohawk, Samurai, Decapitator, Hangman, Archer, Juice, Doc, Punk Biker, Soldier & Slasher.