Sonic & Knuckles is an unauthorized sequel.
Amy could have been playable in these titlesShe was meant to be playable in Sonic CD
Sonic's modern look and powers are side effects of turning Hyper Sonic.As Hyper Sonic, his eyes turned green, just like his modern look. Sonic 4, taking place after this, is the first canon appearance of the modern look and the homing attack. The biggest evidence is that as Hyper Sonic, he could unleash a double jump attack the propelled him further and destroyed any minor enemies on screen, and with the general ability to direct his momentum, and now the boosting he's clearly growing in power.
The asteroids in the Doomsday Zone are chunks of earth and pieces of the Sky Sanctuary that the Death Egg kicked up during its ascent.How else does one explain asteroids in orbit above the earth?
In the Special Stages everytime you do the Orb Turns Into Rings thing someone is getting hit and losing rings.Exactly what it says on the tin