Method to defeat him
To defeat him, dodge his yellow-orange fireballs, jump on him five times, and he'll be defeated.
After defeated by Mario, he turns good again.
—Let us outta here., Luigi to Wario.
Daisy: Please Luigi, I don't wanna fight you. I don't want to do this!
Luigi: I want to DO THIS!!!
Mario: Please Luigi give up now.
Luigi: I will never give up!
Mario: Now it's-a time, everyone. (Fireballs Luigi)
Luigi: ARGH!!!!!!!!!!(turns good again)