Something that I think it would make card system a little bit better is that if there was a NPC that could exchange an X amount of the same card for a OCA for example.
The main reason behind this suggestion is that a lot of players farm mag_dun (including me) and all of us have a bunch of copies of Nightmare Terror, Diabolik and Deleter cards.
In my opinion that X amount required for the exchange could be 10, since the market value of the OCA is around 3,5M zeny, I don't think it would be a meta shifting way to get money or something like that, but instead we would at least have some usage
