An idea that occurred to me for the very distant future is that during the story mode you could face the evil versions of the characters between which you go through the stages.
Let me explain, while we play the mod in theory there are 7 characters (if we count the new unknown character and discount the one we are currently playing) and there is also supposed to be a new stage, if an evil version is made for each one we could face it in an intermediate stage in which it would be just after passing a normal stage, there we would find all the characters in their evil version, dancing in the background (some animations from the sound test could be reused from here), we would notice that one or two characters would be missing in the background (depending on the stage) which we would face right there, as we progress we will face more difficult evil versions while we see how one by one they disappear from the background, as we are supposed to face each time a stronger evil character I came up with this order (the replacement occurs if the character has already been used, either because it was the replacement of the other or because we are using it n us in the game)
(after stage 1): evil cream (replacement: evil tails)
(after stage 2): evil tails (replacement: evil zu) and evil zu (replacement: evil [new character])
(after stage 3): evil blaze (replacement: evil amy) and evil [new character] (replacement: evil rouge)
(after stage 4): evil amy (replacement: evil zeta) and evil rouge (replacement: evil zeta)
(after stage 5): evil zeta (replacement: big)
(as I was writing this I realized that this order completely prevents you from facing zeta last, you would always have big as the last enemy, it's not what I expected to achieve but I think that as it is it's fine)