TCG YouTuber Wossy Plays explains more here: What is the standard Lorcana deck size
Dominaria United s Relic is just great in normal decks, let alone ones where nearly every creature is legendary
Like black, it has a plethora of ways to dish out a lot of tokens, usually Goblins
Mithril Coat Taking Darksteel Plate, giving it flash, and letting it attach itself to a legendary creature when it enters the battlefield makes Mithril Coat an incredibly potent card for any deck where your commander is a creature that ends up dying a lot
This rotational flipping was their solution back in Kamigawa block
Effectively, each player opens a pack, takes a card out, then passes that pack to the next player, and you do this until you have no cards left