Bowser

Bowser is a major character in Avengers: Endgame and is a reformed villain from the 2012 film "The Avengeres". He is also Mario's former archnemesis. Despite his menacing appearance, Bowser gives off a gentle, calming aura and can be extremely intelligent and helpful. Being a reformed ally of Thanos, he also knows helpful secrets about the titan's plans.

Appearance
Bowser appears to be a large dragon-like creature, with green skin, a tan face and belly, yellow limbs, and a spiny turtle-like shell. He usually wears no clothes besides metal spiny bands around his wrists, shoulders, and neck. He has red hair and two long horns.

Story
Bowser is assumed to be dead throughout the Thanos Arc, as he was last seen on the exploding Dreadnought Galaxy. After he calls Mario during the Dystopia Arc, he reveals that he took a small escape pod from the galaxy and piloted it to Earth, where he spent the last 5 years treking to The Avengers HQ. He guides the Avengers as they re-assemble, and in Act II he is one of the creaters of the Infinity Distorter used to find the Infinity Stones. In Fourside, he tricks Seymour Skinner into giving him the Mani Mani Statue (and the Reality Stone). In Act III he confronts Thanos and even attacks him with the classic "shell spin" attack. He attends Deku's Funeral as well.