I had this idea: Combine every single minigame idea from every JJ2 level you can think off.
You start off with your turtle shell buddy, and use him in various situations which seem clever.(only to have him NEVER come back, but make it in the storyline that you get the turtle shell after some SUPER HARD accomplishment) Anyways, after that, have a mini pinball segment which sends onto this 'grind pole'(This was used in Agent Jackrabbit, a stellar JJ2 Episode BTW) which has some grinding segment, afterwards there is an optional minigameish thing where if you pick the right trigger crate, you get a reward(like a PU or something). After that(or if you skipped it) You have one of those regenerating enemies things where you fend yourself off enemies while trying to get coins to proceed. Anyways, the whole thing is timed(using Jazzmusic's idea) and if they make it, they are rewarded to a treasure room with goodies, 1ups, ammo and other things.
If not, when they reach the closed door they fall into a pit and progress through the episode.