Hammer Bro is a koopa who is a part of Bowser 's Koopa Troop. He appears to be friends with Koopa Troopa. Hammer Bro also has an extremely annoying voice that irritates almost everyone, in the fight he claims to be from Philadelphia.
Hammer Bro is one of the few characters in the show that is a figure like Mario, Peach, and a few others. He looks like a Koopa Troopa with a helmet and a hammer. He has a shell on his back, and has green shoes.
At first he wasn't techincally canon as Luigi was dreaming, but he later reappears for real in "Death of Mario?".
Since he has such an annoying voice, Hammer Bro is found an extremely annoying person. He also is a kiss-up, as shown by the way he was kissing-up to Bowser in "Evil Prevails?".