The Nightosphere is an alternate dimension appearing in "It Came from the Nightosphere," inhabited by Hunson Abadeer and a multitude of other demonic and "deathless" entities. In the episode "It Came from the Nightosphere," a portal between the Nightosphere and Ooo, formed in Marceline's house, led to a place engulfed in fire. Details of the place were eventually exemplified in "Return to the Nightosphere" and "Daddy's Little Monster," where it was viewed to be a demonic wasteland filled with chaos. The dimension can be escaped by going through a portal in Hunson's house.
"Maloso vobiscum et cum spiritum" roughly translates from Latin to: "Evil be with you and with your spirit." This phrase may be a reference to the Catholic liturgy, where the priest says "Dominus vobiscum" ("The Lord be with you"), and the congregation responds "et cum spiritu tuo" ("and with your spirit").
The Nightosphere bears similarities to Hell in appearance, and Finn states, "I'll see you in the Nightosphere, you sick freak." This is similar to the known phrase, "I'll see you in Hell."
The Nightosphere also exists in the gender-swapped universe, as Marshall Lee claims to be from there.