It woud be good to have somekind of cross checking that shows what unique cards overlap with co-op players decks, so that they can modify them accordingly. As much as this might be a bit frustrating on occasion, I think it's better than the Theme breaking situations that would come up otherwise (since this is a very thematic narrative game, this is very important!) My personal suggestion would be that Uniqueness should be for the whole board (except for Heros), if my partner plays Erkenbrand or Sting then I can't play them myself.

This gets more complex when you think of Unique Items, for example: If I play sting on one of my heros, can my partner also play sting on another one of my heros? If so, could they play multiple copies on my heros so I end up with all three having Sting? If my opponent has an Erkenbrand, can I play one too? Can I play multiple Erkendbrands on my own side, or will it be one per player? I understand that it is a necessary evil to allow duplicate heros (at least until the card pool is larger!), however what will happen with Allies and Items? I've just been wondering how characters/items with the Unique symbol will work in Co-op?

Co op two player card game