Foil cards appear to be identical to normal cards, except they have a distracting moving rainbow thing on them. I received some from promotional codes. Is there any gameplay benefit to having foil versions of cards, or are they just an artifact from the physical game?
Foil cards are simply cosmetic items, and do not grant any extra gameplay benefits in game.
no, there is totally no difference between normal and foil cards, except for the looks. In real life the foil cards normally cost a bit more than normal ones, because they are "fancier"