Волшебство
В качестве дополнительной стоимости разыгрывания Устранения Соперников пожертвуйте X существ.
Уничтожьте X целевых существ.
If you somehow cast Eliminate the Competition without paying its mana cost, you'll still choose a value for X and sacrifice X creatures.
Once you announce that you're casting Eliminate the Competition, players can't try to remove creatures you'd like to sacrifice.