Gottlieb's Rescue 911 has four white targets on the playfield that serve no purpose. Rumors are that they were meant to spell K-I-R-K for a William Shatner tie-in mode, but it was removed when Shatner's likeliness was not available.
Although Devil's Dare was designed with speech, most machines replaced the original sound/speech board with a sound-only board, leaving the game without any speech or music, and playing slot-machine-style chimes instead.
South Park originally had a "Carpet Munching Race" Video Mode — as Stan, the player competed against Cartman to see who could munch carpet faster and impress Ms. Ellen as the bigger Lesbian. It was disabled soon after the game's release at the insistence of Comedy Central, but ROMs with it re-enabled are available from after-market vendors. Click here for details on the mode.
The basic ("Pro") edition of ACDC omits the Underworld mini-playfield of the higher-end versions, replacing it with a caricature of lead guitarist Angus Young's face.
Pre-release advertisements for Laser War showed off a backbox topper that would display laser light patterns in time to the game action. Unfortunately, it was removed from the final game to cut costs, and only a handful of prototypes exist.