Get 100% completion:
After you beat the game, save when prompted. Then load up the save. You'll be able to go back and complete everything you missed your first time through.
Waluigi Mario:
Put on the W and L emblems.
8-bit room:
In the X-Naut fortress, head to the sublevel 2 ventilation shaft and drop down into the dressing room. Open your stall's curtain to become 8-bit.
Boat parlor game:
Beat Toodles' "I must have that book!" quest.
Paper parlor game:
Beat Pine T. Jr.'s "Save my daddy!" quest.
Plane parlor game:
Beat Koopkook's "Try and find me!" quest.
Tube parlor game:
Beat Frankie's "Important thing" quest.
