According to the Scandinavian manual for Mr. Gimmick, the girl Yumetaro must rescue is named Mary. In all other releases of the game, she is unnamed. During development, she was planned to be named either "Kasumi" or "Ayaka".

The original release of the game in both Japan and Scandinavia contains a track in the sound test called "Strange Memories of Death". This song is not featured anywhere else in the game, implying that whatever purpose it was written for was discarded during development. The arcade remake, Gimmick! EXACT☆MIX, would finally incorporate the song for the new continue screen.

Mr. Gimmick director Tomomi Sakai has claimed that Mario creator Shigeru Miyamoto is a fan of the game:

The original Japanese version of Gimmick contains a unique anti-piracy response where, if the opening cutscene is tampered with, the player will not be able to access the secret final level and it will instead cut to a black screen saying "BLACK HOLE" in reference to the game Atlantis no Nazo. Contrary to popular belief, this was not intended as an anti-piracy method, but rather a failed attempt by game designer Tomomi Sakae to prevent his name from being removed from the opening credits. This trigger was neatly edited around its intended purpose, and was eventually removed in the Scandinavian release of the game, though Sakae's name was reinstated as an unused line of intro text.

In Gimmick: Exact Mix, a black bird ally from the original game was recolored to resemble Kyorochan, the mascot of ChocoBall, a Japanese malt chocolate ball brand similar to Maltesers or Whoppers.

According to the July 1992 issue of Electronic Gaming Monthly, Mr.Gimmick was originally going to be released in the U.S. and was even reviewed, but sadly was never released.

Along with the name of the game being changed from Gimmick to Mr.Gimmick and minor alterations to the music in the European version, the player starts out with 4 lives in the Japanese version while in the English version the player starts out with 9 lives due to the intense difficulty of the game. However, it is easier to get lives in the Japanese version where if the player scores 10,000 points another life occurs at every subsequent 20,000 points, rather than 25,000 points in the European version.