The third bonus content for the mod (Do not forget that the main purpose of the mod is Time Attack, and achievements and medals are just additional content)
I would like to add some hidden images, Sonic CD did it. For example, I could add an interface to select a stage through the code. When you enter a certain code, you are sent to another menu with this image. Or, for example, do the same, only by entering the code in the mini-game menu.
I'm not sure how many images are required. If imagine that to enter a certain image, you will need to get all the medals, or medals of a certain type (which will be more difficult to implement), then I would make 2 images for the first row of achievement medals, 2 more for the second row, and 6 images for all medals of the record type of any character.
I definitely want to include Majin Sonic in the list of hidden images, and probably something not so ordinary will be needed to open it. As for the other images, they will probably be drawn by me, and stylized to match the style of the medals received.