Duel for Dominance
Instant
Coven — Choose target creature you control and target creature you don't control. If you control three or more creatures with different powers, put a +1/+1 counter on the chosen creature you control. Then the chosen creatures fight each other. (Each deals damage equal to its power to the other.)
Ryan Pancoast
Rulings
If you control three or more creatures with different powers and the target creature you control is still a legal target as Duel for Dominance resolves but the target creature you don't control isn't, you will still put a +1/+1 counter on the creature you control. It isn't much of a duel, but your creature is still dominant.
(wotc • 2021-09-24)
Only the +1/+1 counter is contingent on having three or more creatures with different powers. The target creatures will still fight even if you don't have three or more creatures with different powers when Duel for Dominance resolves.
(wotc • 2021-09-24)
Rulings
If you control three or more creatures with different powers and the target creature you control is still a legal target as Duel for Dominance resolves but the target creature you don't control isn't, you will still put a +1/+1 counter on the creature you control. It isn't much of a duel, but your creature is still dominant.
(wotc • 2021-09-24)
Only the +1/+1 counter is contingent on having three or more creatures with different powers. The target creatures will still fight even if you don't have three or more creatures with different powers when Duel for Dominance resolves.
(wotc • 2021-09-24)