Mesmeric Sliver [Future Sight] 170 as if summer still lingered

as if summer still lingered in Elrond's gardens

Set: Sun & Moon: Crimson Invasion Type: Dragon Rarity: Secret Rare Retreat cost: Colorless

Morph {4}{R}{R} (You may cast this card face down as a 2/2 creature for {3}

what is that

You may cast a spell with mana value X or less from among cards revealed this way without paying its mana cost

Mesmeric Sliver [Future Sight] 170 as if summer still lingeredSet: Future Sight Type: Creature Sliver Rarity: Common Cost: {3}{U} All Slivers have "When this permanent enters the battlefield, you may fateseal 1." (To fateseal 1, its controller looks at the top card of an opponent's library, then they may put that card on the bottom of that library.)