You can't cast Hunter's Edge unless you choose both a creature you control and a creature you don't control as targets.
2020-06-23
If either creature is an illegal target as Hunter's Edge tries to resolve, the creature you control won't deal damage.
2020-06-23
If the creature you don't control is an illegal target as Hunter's Edge tries to resolve but the creature you control is a legal target, you just put a +1/+1 counter on the creature you control.
Put a +1/+1 counter on target creature you control. Then that creature deals damage equal to its power to target creature you don't control.
