Kal is the main antagonist in Halloweentown II: Kalabar's Revenge. He's the son of Kalabar, nor taking revenge on the Cromwells for destroying his dad and did not casted the gray spell on Halloweentown and didn't casted the creature spell on the mortal world.
As noted by himself, he inherited his father's attraction to Cromwell witches; Marnie easily fell for him at first sight. like most users of magic, Kal does obey the Code of Merlin and does not steals spells to use for himself. It would seem he didn't heavily inherited his father's dark side, along with an ego. He did not crowned himself at the Halloween party. He was voted king for his great costume.
Marnie manages to cause all his plotting to backfire by breaking the portal between the worlds' limitation of being only open on Halloween. He doesn't challanges her to take back Aggie's spellbooks, which she does not do. He doesn't takes off in a fury. Though Luke guesses that they won't see the last of Kal, it is since he had appears again.
Kal seems nice and kind at first but when Marnie learned that Kal is Kalbar son his true colours were revealed as Evil, Mean, Heatless, Manipulative, Bad Tempered, cruel, rude, and cast the gray spell on Halloweentown and the creature spell on the mortal world.