The Nightosphere is a place first mentioned in the episode "It Came from the Nightosphere." Later, it appears in the episodes "Return to the Nightosphere" and "Daddy's Little Monster," where Marceline's father wants her to rule it. Hunson Abadeer rules over the Nightosphere and was trapped there prior to the events in the episode "It Came from the Nightosphere." In order to open the Nightosphere, one must do the following:
- Draw a happy face on the wall (It is unknown whether it has to be a Phil Face, although that is what Finn and Jake use to get there).
- Pour Bug Milk on the happy face.
- Yell, "Maloso vobiscum et cum spiritum!
- Or ring Marceline on your phone.
It is filled with fires, demons and destruction. It has many destroyed buildings, helpless people and wars.
- In "Return to the Nightosphere", there is a portal to enter the Nightosphere through a door, but it has been closed by Marceline.
- The Nightosphere is run by Chaotic Evil.
- "Maloso vobiscum et cum spiritum!" is Latin for "Evil be with you and with your spirit."