This one is a little weak but pretty important. If you play as Tails in
Sonic 3 + Knuckles and you win, you can play as Tails in Sonic and Knuckles
direcly afterwards. I'm not sure what happens with Sonic and Tails...
Start Sonic World from the main menu by pressing and holding Start + A. You'll enter a new Sonic World challenge where you'll need to collect all 100 rings in an insane 60 seconds. Possible? Barely...