Atemsis, All-Seeing
Legendary Creature — Sphinx
Flying
, 
: Draw two cards, then discard a card.
Whenever Atemsis, All-Seeing deals damage to an opponent, you may reveal your hand. If cards with at least six different converted mana costs are revealed this way, that player loses the game.
Illustrated by
Core Set 2020 Promos#46sRareEnglishLegality
Rulings
Every Magic card has exactly one converted mana cost. A card with no mana cost has a converted mana cost of 0, and 0 can be one of the six converted mana costs that count toward Atemsis’s ability.
If a card in your hand has 
in its mana cost, the value of X is considered to be 0.
The converted mana cost of a split card is determined by combining its two halves. For example, the converted mana cost of Fire//Ice in your hand is 4.
If an effect causes you to play with your hand revealed, you can still reveal your hand as Atemsis’s last ability resolves. The ability works as normal.