I now have several curse cleansing cards. They do not stack and each takes an inventory slot. I have no idea what curses are, how they work, or where to get them. Do they kick in during legendary levels? Are "curses" good or bad?
Curses come from applying stacks of cards to items. It's random, one-way, and it doesn't overwrite. Curses are potentially nice, but there's a raft of dull pointless ones in the table. If you have a great item (reaper + mythic) with a bad curse, the cleanse permits you to try again for a better curse.
Stacks of cards come as Saga Rewards. If you're using your sagas for XP stones, you won't get cards (and vice-versa). It's a system for characters that have full epic PLs and pretty much never need saga stones for a quick epic PL.
My characters don't have full epic PLs, so no curses for me. The XP is too valuable on ER cycles.
IIRC, I have 3 or 4 cleanse cards in bank awaiting the day 10y or so from now when my chars are done with epic PLs.