I'll just explain a brief summary of the idea, since it's basic.exe creepypasta stuff.

3 friends play Sonic Mania, select Sonic, Tails, And Knuckles, get sucked into the game, get ripped apart by The Poacher. Another friend comes across the game, selects Ray, sucked into the game, found by The Poacher, thrown out of the game, killed due to a broken neck and spine from the force. The brother of one of the friends goes to the house, plays the game as Mighty, finds Eggman locked up. After releasing Eggman, Mighty continues foward with Eggman following, eventually finding the remains of the other characters. Continuing foward into Stardust Speedway, they find a bloody mess of flesh and bone stitched together, being what remains of The Poacher. Metal Sonic, covered in blood and decorated with pieces of his victims, lunges out of the shadows near the bloody mess, attacking Mighty and Eggman. It ends with Eggman sneaking away to get the Eggmobile until eventually using the wrecking ball to crush and destroy Metal. The souls are let free, and the brother leaves the game, going back to the real world.

'The Poacher' is the rogue Metal Sonic that set out on a mission to kill not just Sonic and his friends, but Eggman as well. Metal killed Eggman first, before removing his organs and stitching him together to make a disguise out of his flesh, creating the name 'The Poacher'.