絶滅の契機

If a creature on the battlefield has {X} in its mana cost, X is considered to be 0.

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.

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.