He's a hero who fights crime. He went into the city where Fire Mario and Lego Mario live to help defeat the zombies. Due to his black suit, he's attacked by Mini Wario, as he claims that the color black is a sign of evil. But the way he said it seemed so racist. He even attacked him, but Mini Wario didn't get arrested just yet. The bad part is he felt for the corruption of Zombicon and became security for it. When Mini Wario went to attack Isabelle, he was finally arrested.
However it seems Mini Wario escaped. And it also seems Batman himself is not able to get rid of these people. Fire Mario now even dislikes him as well.