Erebus is the first layer of the Underworld route — a cave-like region shrouded in purple mist and moonlight. It serves as Melinoë's first proving ground each run, with 8–10 rooms before the boss encounter that gates progress deeper into the underworld.

Hecate, Melinoë's mentor and the queen of witches, guards Erebus. She fights across three phases using tracking orbs, teleporting attacks, illusion duplicates, and a screen-wide AoE in her final phase.

Erebus is the easiest layer and is ideal for testing new builds. Resources gathered here include Nightshade Seeds, Bones, Bad Dreams, Moon Dust, and Silver. Arachne may appear randomly to offer armor-granting outfits. Charon's shop appears in gold-marked rooms. Prioritize Magick management against Hecate — running out of Magick mid-fight sharply reduces your ability to deal damage.