Barrier can bring a game to an absolute grinding halt
Because there are a lot of cards from TAG that they haven't done so with yet (several OOYAMA trainer cards, well over a dozen full arts, over half a dozen rainbows and 6 other golden Tag Teams) EDIT: In particular, I want TPCi to at least bring over the other versions of Dusknoir-Trevenant
There are decks that are trying to assemble a lot of mana and go way over the top of other decks in the format
Six lands aren't hard to come by in most Magic formats these days
If that creature spell has flash, you'll be able to cast it any time you could cast an instant, even on an opponent's turn
Without any piece of pressure, I would mulligan this hand on the play but keep on the draw, aiming to take on the control role while I find my threats