Mahroe

Mahroe is the true main antagonist during the first parts of Super Mario Chronicles Arc 1: Bowser and Mahroe Saga.

Super Mario Chronicles Arc 1: Chapter 1
Mahroe is shown to be imprisoned on a Helicopter. After the mask has been removed by his head, he states to the people on the plane that he plans to "crash the plane". Mahroe does so killing a few people onboard and the rest while kidnapping Dr. Palma for experimental devices.

Mahroe shows up later and frees Bowser from the dungeon, but soon mind controls Bowser to become his Herald, thus becoming the true main antagonist in the first saga.

Super Mario Chronicles Arc 1: Chapter 2
Mahroe appears in Mario's dream sequence as he had 3 followers / heralds with him which were Bowser, Sonic The Hedgehog and Mega Man. As he was ready attempt to kill Mario in the dream, and in real life. He was too late as Mario was saved by Baxter from the Nightmare Sequence.

Mahroe also returns in with Bowser to his side and traps Red Toad and Green Toad in a portal, and leaves quickly with Bowser while the Toads are rescued by Princess Peach.

He reappears later with his armor fully off talking about his plan to himself, until his wife Mahlaraze tells him lunch is ready as he walks downstairs.