He is a clone of Wario. He's basically a mini version of Wario as well. He is just as dumb, and doesn't follow rules. He stole Ronald McDonald's sign, and broke a law. He is so crazy he argued with himself, until he realized his other self wasn't real. He's pretty over powered, and beat the crap out of Cone Head and Yeti once for stealing money.
He believes the colors red and black are colors of evil. He insulted and attacked Batman due to his black suit. He does have a kind side and was willing to help Fire Mario attack Isabelle for her corruption. He has become more and more useful for Fire Mario, and was willing to attack Cone Head. It unfortunately failed, but it's the fact he was willing to try. No matter how nice he sometimes is, he will also always be rude. Bart at a party kept begging for food, and he told him to stop crying and insulted him.
Intelligent
As it turns out though, Mini Wario is intelligent, stated by Zack Max. In The Walking Dead of Life season 2 finale (episode 11), Mini Wario gets a rock thrown at him when everyone is arguing and trying to safe Fire Mario. This causes Mini Wario to remember who he really is. He acts normal. He talks to everyone normally and attempts to leave the series that is, The Walking Dead of Life. He discovers the creator of the series, Zack Max. He realizes that since he is too intelligent, he must be created stupid so the series isn't ruined. He learns secrets and how many planned seasons there are. Zack Max tricks him into believing that the series is over and they are free. Before he lets him leave, he gives him a cigar to smoke. After rushing back, he tries to save his friends and tells everyone he knows an escape. No one listens because the air in Lost Caverns is lacking. Crazy Dave however, he listens. But now Mini Wario's mind is beginning to fade. Unfortunately he goes back to stupid.