Full Moon's Mist is an enchantment, not an instant.
In the Trivia section of this page, it says the following:
"The werewolf mechanic transform has been designed after Werewolf lore, Humans who turn into monsters when a full moon is present at night. In the game the day and night cycle is represented by the activity of the people playing the game. During the day, people play more spells, but at night people play fewer spells. Werewolves in the set transform accordingly."
This doesn't make any sense! If I'm reading this right, this is saying that people who play Magic: The Gathering at night don't cast as many spells as they would in the morning! What kind of logic is that?