He showed up out of nowhere to Mario. He said he needed his body to conquer the world. He is treated as a joke. He was knocked away by Waluigi. When Mario got stuck, he returned again, talking on how this isn't a joke. Except, once again it's treated like it is. Xavier showed up to distract him. Saying "nice costume" & "it's not Halloween". It gets worse as Wario falls through the ceiling on a couch. After Negative Mario's battle, Marvio went after him. Since Negative Mario has the same DNA as Mario, it works just fine to also needing his body to conquer.
You're Mine Now
Because Negative Mario is stuck in Hell 2.0, he has a higher grand against him. He has to keep using Bloody Fire to take down Negative Mario. Negative Mario tried to scare him away, but it failed. Marvio tried to trick him by throwing a Bloody Fire ball back and fourth then throw it randomly. This also failed too.
This is a power of Marvio's. If it touches Mario or Negative Mario, he can go inside their bodies. It does nothing on other people but them. Walleo even ate one. When Negative Mario blasted Marvio away, he threw one of these still. However, it just disappeared. It barely touched the blast.