Something that's been on my mind recently, was there ever any official reason Amy couldn't curl up like the others? Granted, post Sonic Adventure 2/Sonic Advance 2 she was given that ability but in Sonic Adventure/Sonic Advance 1, she couldn't and I cannot figure the reasoning behind this even from a gameplay standpoint. In Sonic Adventure, she spent most of her time running away from Zero. Even if you did use the hammer to hit him (standing or jumping) the effect was the same. In the case of aerial antics, she could just be somersaulting with the hammer meaning one less button input. Wouldn't change the fact Zero gets immune if hit too many time. Likewise, in Sonic Advance, the lack of curling was just a bad idea. There's no middle ground for that, you are essentially a nerfed Sonic in that game. She plays like her Sonic Adventure counterpart which is bad (the lack of a proper spindash makes going up some inclines impossible) as it doesn't adapt to the classic 2d formula properly making everything in the game (except some boss fights with the hammer whirl) harder than they need to be. My own guess on the matter is that the idea made sense in Sonic Adventure as a way to make her feel unique but didn't work from a design standpoint in the later games (Amy was a SPEED character in Sonic Adventure 3 despite previous games) hence why there isn't much congruence with that design. Storywise, you could just give the excuse that she "learned" how at some point but I'd rather not talk about theoretical story reasons especially when her ability to turn invisible from Sonic 06 will probably never be addressed. That said, if her classic counterpart ever becomes officially playable, I'm expecting her to curl and spindash. Hammer could work like the instashield, not sure how the hammer jump would work though.