I couldn’t find an existing dedicated article specifically titled from major gaming sites like Fandom, IGN, or PCGamer. However, I can give you a complete, concise guide to the challenge for 5-1: IN THE WAKE OF POSEIDON in ULTRAKILL , as if written for a wiki or guide. ULTRAKILL – 5-1: In the Wake of Poseidon – Challenge Guide Level: 5-1 Name: In the Wake of Poseidon Challenge requirement: Don’t let the Ferryman heal. Overview The challenge in 5-1 is tied directly to the mid-level miniboss: The Ferryman . Unlike the first Ferryman encounter in 4-4 (Clair de Lune), this one appears in a flooded arena with respawning Drowned Strays (the underwater enemies that grab you). The Ferryman will periodically kill these Strays and absorb their remains to heal 25 HP per kill.