In Sonic Chaos (also known as "Sonic & Tails" in Japan) for the Game Gear and Master System, Sonic and Tails were facing the threat of Dr. Robotnik sinking South Island by improperly using the Chaos Emeralds. Sonic and Tails collected the Emeralds before the doctor could, including the red one he already had in his possession and liberated the island of his control once more.

Spinball Time:
In the spin-off Sonic Spinball, Sonic went to Mt. Mobius, which was taken over by Dr. Robotnik and made into his "Veg-o-Fortress". However, Sonic was knocked off of Tails' airplane on the way, causing...