Sonic gets the chaos emeralds. Sonic defeats Eggman. Sonic destroys his evil plans. This never-ending cycle has driven Eggman to insanity. So, he spent hours creating a syringe, which contained a deadly virus. He plunged it into Sonic's arm during a fight, slowly turning him zombiefied.

Now...

Shadow: "Look who we have here... Another survivor."

Tails: "Be careful, guys..."

Mighty: "Hey there!"

Cream: "Hello, stranger! Would you like to join us?"

Rouge: "What's your name, good-lookin?"