Atemsis, All-Seeing is a rare Legendary Creature — Sphinx card from Core Set 2020 Promos (PM20), collector number 46p. Current market price: $0.85 (foil $2.24), 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.