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.