In a dedicated Werewolf deck, Moonmist can be a total blowout. Werewolves are often difficult to play consistently due to the fact that you have to be very conscious of how many spells are played in a turn. Being able to transform whatever Human Werewolves you have for only 2 mana is very powerful. Even better, all Wolves and Werewolves still deal damage, while no other creatures can. In fact, even if you have no creatures on the board at all, it still acts as a two-mana Fog. It can still save you a lot of damage.
If you plan to play any sort of Werewolf deck, Moonmist is definitely a strong card. Any copies you find laying around for dimes and quarters at your local game stores should definitely be snapped up in a hurry. While they may reprint Moonmist in Eldritch Moon, it’s unlikely as Werewolves haven’t exactly been super relevant in any competitive format. But they are a lot of fun to play, and the variance of the deck is what makes it so attractive to casual players. Magic continues to support its “fun” tribes quite well recently. So whenever you see a tribe get lots of new support, never overlook synergistic commons. They can suddenly be worth a lot of money.