While underwater treasure levels are okay, I don't find underwater very fun to move around in...it's very clunky. Same with airboards in MP. Half of the fun in jj2 for me is the mobility, platforming and mind games. What I had in mind is smaller platforms, pinball paddles, tubes and vines (not necessarily all at once though, lol) which all work in treasure while you're blinking. However, I actually intend to make a water treasure level someday, but only half of the level will consist of it and would utilise the fun "run and jump insanely high in water" bug.