Deadweed Slugterra : Season 1 Episode 8

Eli doesn't believe in ghosts -- until he enters Deadweed cavern! But it turns out Eli's first instinct was right. What lurks inside Deadweed is far more evil than ghosts, its El Diablus Nacho, after a supply of the dangerous Dark Water that Dr. Blakk uses to turn innocent slugs into Ghouls.