my own ideas for super abilities are already implemented in revi, though sonic's will be replaced in the future since i'm likely changing his main ability again. I think my best, or at least most unique idea from that set is amy's super.
super amy
passive - drain hammer
amy loses rings twice as quickly as other characters while super, but striking an enemy with her hammer will award her a pack of rings. Hearts spawned by the hammer while super will hunt down enemies to drain from.
active - spiral jump
a double jump which reaches incredible heights but cancels your momentum on use.
coincidentally, i've also been trying out a custom supercolor for amy in the next update of my mod. I figured i'd post it here since people were wondering about a pink supercolor.
I really like your ideas for Super Amy. Another thing that could work is replacing the hammer strike with abilities that would make sense for her and still be useful. For example, pressing Shift (or the spindash key) would have her launch herself in the air with her hammer, like she did in Sonic Adventure. Her jump ability could be replaced with a move that has her spin her hammer out to the sides as she drops straight down, damaging enemies on the ground nearby as she lands.
As for Fang, I think it would be funny if his Super basically turned him into a Matrix character. Take away the restriction to stand still to fire, and allow him to fire in the air. If you hold the key down, he could auto target enemies in his vicinity until there are none left. Maybe he could even do some cool poses as he does it. And, of course, boost his bounce ability so he can reach higher areas with it.
---------- Post added at 09:10 PM ---------- Previous post was at 07:13 PM ----------
Going back to the topic of Supers and the mysterious rules of how they work, here's how I interpret it. I could be wrong, but I think the characters who turn yellow (Sonic, Shadow, and Silver) have canon Super forms. All other Super forms are non-canon, hence why they don't change colors, or have their hair change shape. In S3&K and Mania, Tails, Knuckles, Mighty, and Ray get what I consider to be pseudo-Super forms. I think they only exist to give incentive to the player to collect emeralds as those characters. Heck, other games--namely Sonic Advance 1-3--didn't even feel the need to do that much.
Consider how Sonic Heroes handled Team Sonic during the final boss. Sonic goes Super, changing color and shape, while Tails and Knuckles just get a yellow aura surrounding them. I think that was Sonic Team saying, "Yeah, they get enhanced powers, but they're not really Super." I think the same thing happened in the 2D games, and we just didn't realize it at first. For me, the introduction of Mighty and Ray in Mania Plus confirmed it. Super Sonic was the only true Super, because he was a hedgehog. The others didn't change shapes or colors; they just glowed their original colors.