The Mask II (Original Project; Early-Mid 90's)

The Mask was a box-office hit in 1994 and made a genuine star out of Jim Carrey. Getting an animated series and influencing further adaptations (including the original comic book), there were of course talks about a sequel, The Mask II, that would have once again featured Carrey, Amy Yasbeck, and be directed by Chuck Russell. It would have come out just a couple of years later.

However, Jim Carrey made it known that he highly disliked playing the same character twice (as it wasn't "challenging" enough), and turned down a salary of 10 million dollars for reprising the role in this hypothetical The Mask II.

A sequel eventually came out in 2005 as Son Of The Mask, which didn't involve Carrey and was critically panned.

Despite this, there is still some possible evidence that footage of the original sequel project had been shot, or at least some media created. Late video game magazine Nintendo Power (issue unknown at this time) ran a contest in 1995 where the winner would visit the set of The Mask II and even be an extra. It is unlikely that such a contest would be published without at least some significant production being already achieved.

It is unknown about what happened to the winner, but the last issue of Nintendo Power offered an apology to them (as it became an infamous article during their run).