Early in his career, Tim Burton stated his general dislike for sequels (via Last Movie Outpost):

“Sequels are only worthwhile if they give you the opportunity to do something new and interesting. It has to go beyond that, really, because you do the first for the thrill of the unknown. The sequel wipes all that out, so you must explore the next level. I don’t rule out anything if the challenge is exciting.”

Screenwriter Sam Hamm, who co-wrote “Batman,” had developed a screenplay simply titled “Batman 2.” It very much carried on from the events of the first film, following the flourishing romance between Bruce Wayne and reporter Vicki Vale while he also tackled two classic Batman supervillains, Penguin and Catwoman. Hamm originally wanted to chart the downfall of Harvey Dent as he became the fiendish Two-Face, but the studio considered Penguin to be Batman’s biggest foe after Joker.

While Hamm’s script was consistent with the darker tone of the original, it still worked towards a happy ending for the Dark Knight. It concluded with Bruce’s marriage proposal to Vicki and also gave him some company at Wayne Manor in the form of Dick Grayson, in readiness to become Batman’s youthful sidekick Robin.

It hardly sounds like the “next level” Burton spoke about. To appease him, Warner Bros. agreed to bring in screenwriter Daniel Waters, whose work on “Heathers” Burton admired. He was tasked with completely re-writing the script to satisfy a more Burtonesque vision, and he made significant changes to Hamm’s original concept (who still received story credit). He kept Penguin and Catwoman as the chief baddies but scrapped Vicki Vale and created an original character, tycoon Max Shreck, to replace Two-Face. He kept Grayson, but poor Robin was later cut due to the escalating budget.