The Nightmare Series (also known as the Nightmare Universe, the Nightmare Trilogy, and Nightmare Version) is a series of fangames by Jaiz Koys, Mastered Ultra Instinct Kostas and Danuha2526 based on the original Sonic.exe indie game, though it is very different from the original game in many ways, such as having genuine plots and lore. There are currently only six games that have been made, but two more are planned.