Wild Instincts

Oracle Text

Target creature you control gets +2/+2 until end of turn. It fights target creature an opponent controls. (Each deals damage equal to its power to the other.)

Card Rulings

6/22/2015 You must target both a creature you control and a creature an opponent controls to cast Wild Instincts.
6/22/2015 If the creature an opponent controls is an illegal target as Wild Instincts tries to resolve, but the creature you control is still a legal target, the creature you control will get +2/+2, but the creatures won’t fight. Neither creature will deal or be dealt damage during the resolution of Wild Instincts.