You can choose from six Nightfarer classes when you begin your Nightreign adventure, but the Duchess and Revenant are hidden behind some easy steps.

You can unlock the Revenant after you’ve already unlocked the other unlockable character, the Duchess. Once you’ve unlocked Duchess, you’ll be able to get the Besmirched Frame relic, beginning the steps that’ll add the Revenant to your lineup of playable Nightfarers.

For the beginning of the Duchess' Remembrance, you need to first help a concerned Raider: Speak to the Raider in the main Expedition room of the Roundtable Hold. Speak to the Wylder in the small room adjacent to the journal room. Go back to the Raider and talk to him again.