Target creature you control gets +1/+1 until end of turn. It deals damage equal to its power to target creature you don't control.
As Clear Shot tries to resolve, if either creature is an illegal target, the creature you control won't deal damage. If the creature you control is a legal target but the other creature isn't, your creature will still get +1/+1.
You can't cast Clear Shot unless you choose a creature you control and a creature you don't control as targets.