Eels appear to be octopus-like creatures. They are very large, emit a red glow from their eyes, and possess several spots of orange bioluminescence. They are the only darkbane creatures that can pass through the barrier, however in doing so they are saparated from their physical form and become ghost-like, largely transparent and incorporeal.
Eels first appear in "It Comes by Night", when one terrorizes an unnamed cavern. After attacking a number of owned Slugs, Brodie contacts the Shane Gang hoping Eli would use his healer slug to help restore the Slugs' drained energy. Eventually the cavern's town council decides to put a bounty on the creature's head. This draws "Fire & Ice", the Power Triplets and Gerhard Stocker into the fray. After a heavy battle in the forest, the creature flees. Later the cavern residents prepare to fight back with its only weakness: Phosphoro Slugs. This is when Eli Shane lures it into absorbing more slugs, causing it to become solid. Eventually it is brought down by Eli and Gerhard, causing it to release all the energy it previously absorbed. In "Light as Day", it was seen coming out of Dr. Blakk's terraportal and then fighting the Shadow Clan. And it was succeeding until Doc saved the day. In "Return of the Elementals" they helped the Darkbane get to Upright Cavern so they could Ghoul the Fire Elemental.
- Flight - Eels can fly and hover mid-air unaided.
- Strength - Eels are strong enough to easily overpower most velocimorph slugs.
- Durability - Eels can endure hits by velocimorph slugs without much problem, unless those slugs attack via fire or light.
Once Eels pass through the barrier, they are saparated from their physical form and become ghost-like. While in this state, they gain the follwoing additional abilities, which they lose once they regain their physical state.
- Spirit Syphon - Incorporeal Eels are able to drain the spiritual energy of slugs and people with their tentacles. They do so in order to regain their physical state.
- Intangibility - Incorporeal Eels are naturally intangible and therefore cannot be harmed, however can still fully intaract with the physical world.
- It's ability to drain ones spiritual energy may be based on the chupacabra, a creature allegedly living in Latin America that is said to be able to completely drain one's blood.
- In Return of the Elementals, Eli Shane refers to these creatures as Eels.
- Eels see anything that they can drain the energy of, like slugs or people, in bright orange.
- When they die, they release the spirit's of things they have drained.
- Highly non-canonical to the show, the infamous "High Plains Monster" makes an extremely rare return in game form in Slugterra: Slug It Out 2 as an exclusive one-time rare boss battle in story mode.
- Unlike the show where the "High Plains Monster" is seen as a transparent thing to a later dark brownish-blue creature and wreaking havoc in High Plains Cavern, which it's named after, in the game the creature appears as pale milky-white creature in The Dark Periphery.
- Also it can project purple waves that disrupt the brain. It can also summon purple monsters that catch slugs that are flying towards them and take them back to the slugslingers.