Hallowar

"with my newfound powers, i shall destroy the world! kekekekekeh!"

-hallowar

hallowar is the final boss in super DUPER mario bros. he is the soul of Cheo's great (X5) grandfather who died mysteriously. now his motive is to kill all.

backstory
his normal life is unknown. his soul was reinformated when king koopa came from the past. he posseses king koopa when he fights you in his first form. he didn't know why he was alive, but then he realized the purpose of his reincarnation. he snatched king koopa's soul and replaced it with his to become one with a body yet again. mario defeats him and he goes into his second form.

his second form consists of a seemingly ghost spirit with a skull for a head, with glowing eyes.

when you beat him, he joins you're party and can be used to teleport to already- beaten levels if you missed something.