Extinction Event
Sorcery
Choose odd or even. Exile each creature with mana value of the chosen quality. (Zero is even.)
"Nature is more merciless than any hunter I've ever known." —Zai, nightsquad captain
Illustrated by
Ikoria: Lair of Behemoths#88RareEnglishLegality
Rulings
Apr 17, 2020
If a creature on the battlefield has 
in its mana cost, X is considered to be 0.
Apr 17, 2020
You choose odd or even while Extinction Event is resolving. Players can't take any actions between the time you make that choice and the time some creatures go extinct.
Apr 17, 2020
The mana value of a token that isn't a copy of another object is 0. A token that is a copy of another object has the same mana cost as that object.