Showcase

Showcase cards were introduced in Throne of Eldraine. Showcase is not one treatment but a catch-all term to cover a variety of different treatments of cards that embody the spirit of the relevant sets. On showcase cards, the art and card frame play into the set's theme.

Description
Each set has its own unique showcase cards. Which cards get the treatment (and usually, it will just be cards from that set), and at what rarity, will vary from set to set. Showcase cards replace cards of the same rarity as the non showcase card in booster packs. The showcase cards don't require a mechanic to correlate with a new frame. It can be any theme.