Inside the game's files is an unused image of Jeffrey Dahmer holding a paper bag with the head of Neil Nicastro (executive producer, and CEO of Midway Games until 2004) in it. The image appears several times in various sizes, and was most likely used to fill empty space in the game's data.

There are two versions of the boss "Junior". In the arcade machine is a switch that will change the boss of the Freak Show from a big baby to a gigantic teddy bear named Deaddy. It's likely that the switch was added to avoid complaints from parents regarding the shooting of an infant child.

In the game’s "Freak Show" level, the player enters the "Museum of the Slightly Curious", which features odd antiques like "Salty Jack" (a reference to the mascot for the snack food Cracker Jack) and the "Horse With No Mane" (a pun referencing the 1971 song "A Horse with No Name" by folk rock band America). One of these antiques on display right below a health power-up is a caveman "Frozen in Time!".

The cartoonish, one-eyed Caveman is actually the titular enemy character from the 1991 Midway arcade game Trog. The inclusion was a reference to CarnEvil's Director and Lead Designer Jack E. Haeger also serving as the artist for Trog.