2020-06-23
If the creature you control is an illegal target as Primal Might tries to resolve, no creature gets +X/+X. If that creature is a legal target but the creature you don't control isn't, it still gets +X/+X.
2020-06-23
If you choose two target creatures and either target is an illegal target as Primal Might tries to resolve, neither creature will deal or be dealt damage.
2020-06-23
You can cast Primal Might targeting only the creature you control.
2020-06-23
You can cast Primal Might with 0 as the value of X to just have the two target creatures fight.