Sometimes, you may experience death in the RPG. Dying will set you back in XP and also progress, as you get sent back to the starting area of the world. Another thing that'll happen is your spirit on death will become a revenant, a monster with a copy of your skills on death. Anyone can fight these, but once they're fought and defeated they will disappear from the world forever.
Revenants will drop a random material from a list, primarily Nightmare bases, and they will drop a random equipment piece from whatever the revenant had equipped on death.
If you see one, perhaps your own or another adventurer's - you can fight it by standing on the same tile and using the command !revenant. It'll prompt you with the level of the revenant, and you can decide whether or not you want to fight it.