Dab
The Dab Glitch, or shortly Dab, is a celebration animation glitch which allows Mario's head pitch and yaw to be stored from C Up Camera mode to the celebration animation after collecting a key, making the animation look strange due to Mario's head facing into a direction different from its default position. This glitch is only possible on the J 1.0 version of the game as it was fixed in the English version or later.
Execution
After beating Bowser in the first or the second battle and activating Bowser's death animation by finishing reading the textbox, move Mario directly under the dying Bowser to stand in the same spot where the key will drop. Then go into C Up Camera mode to change which way Mario's head will be facing. Mario's head will be stuck facing the same direction the moment when the key becomes tangible after it finishes bouncing.