Hacks of games online is nothing new. It's when something becomes an online phenomenon that most people begin to take notice. Sonic.EXE is one of those games. It fits with the Halloween theme, and I'll tell you why.
Sonic.EXE almost looks like a normal Sonic game, until you press start, then for a split second, the screen turns red. You control Tails, Knuckles, and Eggman in a losing effort to get away from a demonic Sonic. Basically, there is no way to stave off death. Sonic will get you inevitably.
The game begins with Tails happily skipping through a level until you see mutilated animals scattered on the ground. He then see Sonic, and the screen changes. Tails is now running from his best friend in the whole world! Accompanied by the drowning music, Tails runs from Sonic until Sonic teleports in front of Tails, ending his game. Next is Knuckles' game, where he has to run as well before Sonic inevitably kills him, too.
Next, you play as Sonic's arch enemy, Eggman. Eggman is running without the aid of one of his vehicles, his thin legs carrying his big frame. Eggman runs a little longer than Tails and Knuckles until Sonic appears and kills him, too. After that, an evil looking Sonic appears and says, "I AM GOD!" With a taunting laugh, a message on the screen says, "Ready for round 2?" Than a horrifying "game over" screen.
There's a creepy story told about it on the Creepypasta wiki; a fascinating read! As for the game, just do a search. You'll find it.