Dark Energy also known as Ghoul Energy is energy that's given off of Ghoul Slugs and Dark Water, but is naturally found in the Deep Caverns.
- Source of life and power for creatures from the Deep Caverns and things that have been corrupted.
- Being surrounded by Dark Energy prevents regular Slugs from transforming at velocity.
- Overtime normal Slugs feel ill, and can die.
- Items powered by Ghoul Energy have a reddish glow as opposed to things powered by Slug Energy, which is blue.
- Exposure to Dark Energy can cause changes to a living being, such as the skin to turn ghostly white like Dr. Blakk in Back to Blakk, to be mutated into a monster like Dr. Blakk in Slugterra: Return of the Elementals, or gain immortality and other dark abilities like The Emperor as revealed in The Fall of the Eastern Champion.
- Powers Mecha Beasts that have been ghouled and makes them defective and explosive as seen in Mecha Mutiny.
- Used to create and power Terraportals, so far only to the Deep Caverns.
- It can also be used to twist and corrupt slugs and mind-control other living things (slingers/humans, Ogres, etc), if ghouling them is impossible.
- Perform Dark Magic such as enhancing a Ghoul Slug, creating automatons and weapons, even draining life force from a living being.