The first of these cooperative battlers is subtitled Deep Trouble, and it seems as though we can expect a series of these PvE-style releases in future sets
FCA cards are legal in Commander, Legacy, and Vintage, and each card is also legal in any other format where its already legal (e.g., Lightning Bolt is Modern-legal)
Additionally, the fact you gain a lore for playing it is pretty broken
Gilded Lotus isn't the most valuable bonus card we've ever seen, but its art is still gorgeous enough to likely be worth getting a hold of
Furthermore, Fabled will introduce reprinted cards from earlier sets - like Winnie the Pooh (Hunny Wizard) - and those will be fully usable in competitive play
But then he transforms into One-Winged Angel, and his power becomes all too clear