Sonic the Hedgehog 3 doesn't hit theatres until December 20 but spoilers have already leaked online, including of its end credits scene which sets up a fourth film. As reported by Kotaku ...

But I'd promised to accompany Bobby to the long-anticipated "Sonic the Hedgehog 2," and I ... t want it to end. He's usually impatient and bolts for the exit as soon as the credits roll.