-Batman Forever was the 3rd "modern" Batman film that came out in 1995, following Batman Returns. It would go on to star Val Kilmer as Batman, Chris O'Donnell as Robin, Tommy Lee Jones as Two-Face, Jim Carey as The Riddler, Nicole Kidman as Chase Meridian, Drew Barrymore as Sugar, and Debi Mazar as Spice. Joel Schumacher would direct and thus the first gay director to direct a superhero film.
-Tim Burton and Michael Keaton were originally due to return but after Batman Returns made less than Batman WB chose to get rid of Burton as they blamed the darker take on Batman as the reason why the film didnt succeed its predecessor. With a decision to take the franchise in a more "family friendly" route, Keaton ended up dropping out.
-With Keaton/Burton leaving the film it caused a domino effect of further casting changes. Rene Russo was originally set to play love interest Chase Meridian but once Val Kilmer was cast she was deemed to old and thus the role went to Nicole Kidman. Russo was 5 years older than Kilmer while Kidman is 8 years younger than Kilmer. Marlon Wayans was attached to play Dick Grayson/Robin but was let go in favor of Chris O'Donnell.
-Once filming begun they ran into multiple issues with Val Kilmer and Tommy Lee Jones. Schumacher called Kilmer "psychotic" and TLJ a troublemaker.
-Val Kilmer clashed with Schumacher to the point of refusing to speak to him for a solid 2 weeks during filming and allegedly ripping off his Batman cowl out of frustration. He allegedly went off on cameramen and first AD, costuming department, and created a hostile work environment whenever he was on set.
-Tommy Lee Jones was allegedly jealous of Jim Carey stealing scenes from him when they would film together and was thus very rude and unprofessional whenever they were around one another. Things escalated to the point where Jim Carey was approached by TLJ who stated " hate you. I really don't like you... I cannot sanction your buffoonery"
-After Batman Forever came out, it was deemed a success as it went on to make more than Batman Returns but Val Kilmer allegedly refused to return for the sequel as he felt anyone could play Batman and was not happy that Warren Buffets children appeared to be more impressed with The Batmobile than him when they visited set.
Source: 1 2 3