If possible maybe you could add character selecting? For instance when making a level you could decide which character the level is meant to be played as.
For example there could be levels that you're supposed to play as Tails and literally cannot do with Sonic.
I think it'd be a cool concept, and even adding another character (like Tails) would be a hell of a lot of work.
Edit: There's a few bugs (obviously), one of which: The ring box doesn't work, and anything touching it makes Sonic fly upwards.
I made a staircase leading up to a ring box and it just telported Sonic to the ring box and made him start teleporting up and fall back on the ring box.