Quote from arrogantAxolotl »This. When I first saw this card, I didn't think twice about it. Then I played against it. Absolute powerhouse. Nigh impossible to destroy too since it can change its card type to dodge removal.
I hate to burst your bubble, but no it cannot. Once Mirage Mirror becomes a copy of another permanent, it loses it's ability to copy stuff until end of turn. The card is still an absolute house, but it is not so good that it can copy permanents at will. So while you may have an issue destroying it while it sits unused, once the activated ability resolves it is vulnerable.