Can you cast reflector mage if your opponent has no creatures in play as just a 2/3 body?
Yes.
Creature spells don’t have targets. They can never have targets. There’s never a situation in which you’re barred from casting a creature spell simply because you wouldn’t have a target for its ETB trigger.
In the case of Reflector Mage, it would enter the battlefield and trigger, but then the trigger would never go on the stack because there aren’t any targets for it.














