Eliminate the Competition
Sorcery
As an additional cost to cast this spell, sacrifice X creatures.
Destroy X target creatures.
Open hostilities are strictly forbidden at the Inventors' Fair, but "accidents" still happen.
Joseph Meehan
Rulings
If you somehow cast Eliminate the Competition without paying its mana cost, you'll still choose a value for X and sacrifice X creatures.
(wotc • 2016-09-20)
Once you announce that you're casting Eliminate the Competition, players can't try to remove creatures you'd like to sacrifice.
(wotc • 2016-09-20)
Rulings
If you somehow cast Eliminate the Competition without paying its mana cost, you'll still choose a value for X and sacrifice X creatures.
(wotc • 2016-09-20)
Once you announce that you're casting Eliminate the Competition, players can't try to remove creatures you'd like to sacrifice.
(wotc • 2016-09-20)