2014-09-20 : If either target is an illegal target when Swift Kick tries to resolve, neither creature will deal or be dealt damage.

2014-09-20 : If just the creature you control is an illegal target when Swift Kick tries to resolve, it won’t get +1/+0 until end of turn. If the creature you control is a legal target but the creature you don’t control isn’t, the creature you control will get +1/+0 until end of turn.

2014-09-20 : You can’t cast Swift Kick unless you target both a creature you control and a creature you don’t control.