Undertale Timeline Collapse - Nightmare Sans Boss(Successful Solo) 

To Summon Nightmare, Find A Corrupted Apple(Black Apple) In The Dreamtale Area.
It Drops From The Tree Every 15 Minutes With A 25% Chance To Be Corrupted, 25% Chance To Be Pure, and 25% Chance To Be Normal.
If You Have Completed Nightmare Quest 1/Dream Quest 1 That Is Given Out By Jester At The End of Judgement Corridor, You Can Summon A Corrupted/Pure Apple With A 25% Chance for Either or 75% For Normal.
Upon The Apple Spawning, It Stays Spawned For Around 1 Minute, So Use It Quickly.
Depending on How Laggy You Are Is If You Can Beat It.