The deepest corners of Greece are filled with all things terrible, which is perfect for a witch like Melinoë. In Hades 2, Nightmare is a kind of collectible, but it may seem impossible to find – for a while.
Hades 2 HOW TO EASILY GET A NIGHTMARE (N.Mare Material) – Hades 2 Fear System Explained
You’ll primarily find Nightmare by completing tasks for the Oath of the Unseen, a difficulty modifier system you unlock after killing Chronos in Hades 2. Check your Oath of the Unseen board and make sure you have the weapon and fear required to make the portrait fully colored. As long as you have fear, though, there’s a chance you’ll find Nightmare during your runs. You can also purchase one from the Broker for 1,000 Bones.
Nightmare becomes quite common during Fear runs, but only for the exceptionally lucky. There are three ways to get a Nightmare drop, guaranteed.
The game mentions that you have a chance of getting a nightmare during high difficulty runs, but we haven't had that luck yet.