Moona is a moon fairy from the moon. She helped Blue find a key, then a lock (found on a box) to use it on, which unlocks a special room. Inside the room, Blue is able to talk and walk on her hind legs. Moona is usually seen at the beginning and end of every Blue's Room segment of Blue's Clues and almost all the Blue's Room episodes and shorts: 1st when she transitions to the Blue's Room segment/starts the episode, 2nd when she tells Blue that it is time to leave and go see Joe (the latter usually applies for Blue's Clues episodes), and 3rd when she transitions from the Blue's Room segment/ends the episode.
Moona has an aquamarine head with sparkly deep sky blue hair shown as a pair of crescent-shaped pigtails tied with dodger blue bows. Her body is also sparkly and shaped like a crescent; the "horn" that connects to her head is aqua/cyan, the other is dodger blue, and the rest of the shape is deep sky blue. Connected to the body at the area where the aqua/cyan begins to mix with the deep sky blue are a pair of sparkling neon blue arms with sparkling aquamarine hands; the left one holds a long, slightly curved, sparkling dodger blue wand topped with a sparkling deep sky blue crescent moon. She leaves a trail of stars in various shades of blue wherever she goes.
Moona appeared in every Blue's Room episode, and all the Blue's Room segments of Season 6 of Blue's Clues.