mtg demon support cards of Loathing - Theros Beyond Death you may cast an enchantment spell by paying life equal to its mana value rather than paying its mana cost. Demon of Fate's Design

Creature - Dragon Horror Elder Brain Menace Whenever this creature attacks a player, exile all cards from that player's hand, then they draw that many cards

It's mostly used in the same way that people use Burning Wish and Cunning Wish in Legacy: it can find a potentially game-winning combo piece but also a ton of unique answers like Fracturing Gust, Firespout, Slaughter Games, Flesh / Blood and Wear / Tear

Soulherder, Teleportation Circle, and Thassa, Deep-Dwelling are all cheaper and better, but not every deck can run them or wait until the end step

In fact, I've played all but 5 cards in the Blue and White genre