Press Y for Hattie (Luigi's now canon Cappy) and the Arrow Keys for Movement. The Hat Dive is triggered by Jump, Hatty, and after that hold Y, Up, and Down at the same time. Do it twice for more air.
Thanks to @FunnyAnimatorJimTV for the base game. These games are back! With my school schedule, they may be few and far between but I'll release as many as I can! I'm excited to work on some more of these :)