If the U.S. version of Sonic CD's Game Over music gave you nightmares, expect night terrors after hearing the Sonic.exe version of it accompanied with Sonic's gruesomely mutilated victims.
Said Game Over screen shows Tails', Knuckles', and Robotnik's heads are severed and their heads posted on wooden stakes with their eyes ripped out. Knuckles' body is hung by hisentrails!!
Sonic's level in Version 5. You have to run through a static, empty void that turns into the seizure-inducing Giygas background with persistent screaming of somebody being tortured heard throughout.
In An Ordinary Sonic 1 ROM Hack, when Sonic is warped into EXE's world, the only way out is to break item monitors. If you happen to reach the end of a level while in dark world mode, instead of the goal you'll find him just laying on the floor, smirking. Even if you walk into him, he does nothing but stare through the fourth wall until his chase mode starts. Better hope the bastard doesn't get you into an unwinnable situation!