You have to click on your cards to find out if they’ve been mastered. Instead, could they have, like an ‘M’ icon displayed on them, or a different border perhaps, so you can see which cards you’ve mastered in your inventory or deck lists?
I’d love to have an awesome gold frame border on mastered cards. Pimped out and stuff. Maybe some diamonds and rubies and emeralds dripping off it. I would get behind that.