Atemsis, All-Seeing is a rare Legendary Creature — Sphinx card from Core Set 2020 (M20), collector number 46. Current market price: $0.46 (foil $0.74), TCGplayer market prices via Scryfall.
Flying {2}{U}, {T}: Draw two cards, then discard a card. Whenever Atemsis deals damage to an opponent, you may reveal your hand. If cards with at least six different mana values are revealed this way, that player loses the game.