From the Super Mario Wiki
Retrieved from "https://www.mariowiki.com/index.php?title=Dr._Demise&oldid=2560194"
Dr. Demise later appears at a museum, using his knowledge of a meteor collision ten years prior along with his knowledge of Kid Dynamo's age to deduce that the meteor dust is what gives him his powers. He steals the dust, then appears at Kid Dynamo's house to kidnap Lightning, his anthropomorphic pet dog. This was actually a trap to lure Kid Dynamo into his hideout, and consequently cause him to lose his powers. When Donkey Kong Jr. and Bones tried to intervene, Dr. Demise simply opened up a trapdoor on them, announcing his intent to rob the next cargo train to depart Sweetville Station.
At Sweetville Station, Dr. Demise instructed his assistant on how to break into the train's cargo hold. Kid Dynamo then appeared, using his restored powers to attack Dr. Demise. The latter eventually crashed his helicopter into a pine tree and was covered in its needles. Kid Dynamo then beat up the helicopter, destroying it and causing Dr. Demise to plummet towards the same train car his now-immobilized assistant was stuck on. His exact fate is left unknown, but he was presumably arrested along with his assistant.