If the face-down creature was an instant or sorcery card, it cant return to the battlefield and simply stays exiled
To build a Magic: The Gathering Arena deck, you'll need to collect all the cards necessary for the deck list (click on the images above each deck in our guide to see the cards you need), then navigate to the 'Decks' area in the game client, create a deck, and add all those cards to it
Unsurprisingly, the set has tons of stuff for Phyrexian fans in this set, especially if you like teeth Phyrexia: All Will Be One has a reasonable spread of solid Cube goodies, and a much deeper well for more niche environments
Itll trigger all manner of payoffs, and while the activated ability is expensive and probably wont be used that often, it might come in clutch from time to time
I like pairing this with cards like Snapcaster Mage and Mizzix's Mastery that let me cast it from my graveyard without paying 8 mana
Once youre in, youll start with the tutorial