A Nightgeist is the Ghouled version of the Frightgeist. When hit by one of these Ghouls, its enemy turns into a coward that runs from almost anything until the effects wear off. Its attack has a longer-lasting effect than its regular counterpart. This Ghoul first appeared in "Deadweed". It is the favourite Ghoul of El Diablos Nacho. Nightgeists can also hit certain creatures that are incorporeal.
- Protoform Abilities - Make you feel creeped out, can be an early warning system of approaching danger.
- Paranoyd - Hits an opponent, creating an uncontrollable fright response. Opponent sees visions of horrifying things.
- Tormentia - Gross, unearthly, ectoplasmic tentacles grab on to a foe and drag them to the ground.
- Ghastling - Bits of gross ectoplasm break off to swarm attack an opponent, slamming them with thousands of tiny punches.
- Tombtwister - Ectoplasmic tentacles latch on and make an opponent intangible, dragging them inside an object to trap them.
- A Nightgeist is featured on the banner image of the official website's 404 page.
- In Slugterra: Slug It Out!, its icon is mistakenly displayed as a Thrasher instead.