Doki Doki Butterfly Effect
Also available as: Android mod
Most mods install on top of a fresh copy of DDLC, free from ddlc.moe. Follow the author's instructions, and keep a clean copy of the game.
About this mod
The mod extends the story after act 3, where the girls are saved. However, the MC notices that the girls have been acting strange as time goes by. Confused, he goes to investigate what happened, but then, "something" hypnotizes him.
Full credits
u/isweartogo-