Yo what if there's the Konami code and when you press A after doing the up up down down left right left right its puts a secret background in that's the green hill zone
or if you do konami code on any character it will have a corresponding backround, gojo will have his domain expansion backround, same for sukuna, sonic will have green hill, same for knuckles and metal sonic, kirby will be in the kirby world map, kendrick will be in the place where they made the not like us music video, and all sorts of stuff like that