Bowser Jr

Prince Bowser Koopa Junior (or simply Bowser Jr.) is Bowser's youngest son, the second-in-command of the Koopa Troop, and the secondary antagonist of the Mario series. He, like his dad, is a dragon-like Koopa with the ability to breathe fire. He first appeared in Super Mario Sunshine, under the guise of Shadow Mario, a strange watery-blue doppleganger of Mario. He uses a Magic Paintbrush forcibly made by Professor E. Gadd, which he uses to spread a nasty, thick paint-like goo all over Isle Delfino, and due to resembling Mario, the hero is blamed and placed under community service and is forbbiden to leave until the island is saved. When Bowser Jr. reveals himself after capturing Princess Peach again, the citizens villains realize they fucking made a mistake and apologize to Mario. After getting all of the Shine Sprites, and getting to the top of Corona Mountain, realizing, of course, Bowser is behind it all. He then kicks his nemesis and second nemesis out off there bath, and causes everyone to fall to their supposed deathes, except for Peach, who has an UMBRELLA!!!!!!. Bowser and Bowser Jr. of course survive the fall, landing on the flipped tub. Bowser then feels it was about time to tell his son the truth, where Bowser Jr. tells him he already knows that, and tells him that when he gets older, he wants beat Mario again, making Bowser proud. He later appears in a bunch of other games.

Mario and Sonic: Worlds in Danger
Bowser Jr. appears as a major villain in Jmkrebs30's Flash series Mario and Sonic Worlds In Danger, alongside Metal Sonic. He, along with his father and Dr. Eggman plan to bring the Mushroom Kingdom and Mobius together. It's confirmed that he will fight Mario, Sonic the Hedgehog, Luigi and Miles "Tails" Prower in a rebuilt Megahammer. It's also confirmed that He and Metal Sonic will fight Mario and Sonic aboard the Death Egg near the end of the series.