McDonald's Treasure Land Adventure
McDonald's Treasure Land Adventure
In the April 2021 issue of the magazine Retro Gamer, Treasure's president Masato Maegawa revealed that entering a specific password on the game's password screen would allow access to a secret "polygonal display". After searching through the game's code and many brute-forced attempts, the method to access the display was eventually discovered:

Enter the password (shown in the attached picture) "Balloons", "Jewel", "M" and "Clown". Then, press Start three times until you hear the sound of an explosion and quickly hold Up+Left and wait. If done correctly, the McDonald's Password sign will turn from a 2D sprite into a 3D model, and the music will change to a song that sounds eerier than the normal password screen music.

•D-Pad = Rotates the model
•B and C buttons = Zooms in and zooms out the model respectively
•Holding A and using the D-Pad = Moves the object across the background
•Holding A and pressing C = Switches the current object with a different one.

The viewable 3D polygonal models in this mode include the McDonald's Password sign, several cubes and squares of varying sizes and dimensions, the box in the Treasure logo, the "S" in the Sega logo, the entire Sega logo as a separate flat model, and a spaceship.
Contributed by MehDeletingLater
In the US version of the game, the magic power up item's graphic is changed. This is possibly due in part to the visual similarities the other localized version's icon has to a sperm.
Contributed by ProtoSnake