You can look up guides on how to unlock the class and that’s easy enough. You need to craft an item at an altar, and it is going to cost you blood moon essence which you can farm from wisps that spawn during a blood moon. What you don’t find online is how to actually spawn the blood moon. I do not have good news here. It seems random and extremely rare. I have tried killing the doe as suggested. No bloodmoon. Travelling back and forth between the ward and yeasha, no bloodmoon. Just walking through doors. No bloodmoon. I did this for hours. SO. It seems like getting the bloodmoon is rare and just pure luck until someone can figure out the mechanics of it.

BUT if you do get a bloodmoon harvest the wisps as fast as you can, and then go through a doorway into a dungeon. Not the crystal, you don’t want to reset the monsters. Just go through a yellow loading door and back and the wisps will respawn. Farm up as many as you can. You need 15 for the class and then there’s an armour set if you want to go for it. I don’t remember how much all that is because I’ve never managed to farm up enough wisps lol. For this character I just happened into a bloodmoon and there weren’t many wisps spawned in. I only saw three, so I just kept moving into the dungeon and back to respawn those three wisps until the bloodmoon was over.

Anyway, I found a lot of guessing online, most of it wrong, about this so at least I can provide some experience. Good luck and good hunting!