If your opponent doesn't pay attention and activates Mirror Wall before the Damage Step (because they have something such as Enemy Controller face-down), then you can. But generally speaking: no, you can't.
I mean, if your opp has a set or two and a mon in face up attack mode, you got a 2/3 chance of it being WoD or M Wall. So throw it down and then attack.
Anoymous
Ulle