If the deck he’s using has deck space/bench space for one you can slot in a Drapion V or Spiritomb, both of which ruin Mew’s day. Otherwise, somewhat viable free decks like Chien-Pao can just try to brute-force break through it, it’s not an impossible matchup.
No, what they mean is that you can search it out with effects like VIP Pass and get its effect, something Dedenne can’t do because it specifies it has to be played from the hand.