Nightmare Fuel is a Refined Item crafted with 4 Dark Petals. A Prestihatitator is required to unlock the recipe. It is also dropped by Beardlings, Crawling Horrors, Terrorbeaks, damaged Clockwork Monsters, and Splumonkeys. It can also be aquired when a Touch Stone breaks and mining Ancient Statues. It has a slim chance to be dug up from Graves and 25% chance to be found in Ornate Chests, and 75% chance to be found in Large Ornate Chests.

In addition to being able to fuel Night Lights, it is used to craft several Magic items.