Cresselia has a series of horns near its head that resemble crescent moons. It has a yellow stripe that stretches from its face to the tail. The rest of its body is blue. It has three pink wings, two under Cresselia and one above it that is lighter in color. When Cresselia is shiny, the pink wings become a teal color, its body becomes purple, and on its forehead, what used to be pink becomes teal.
Cresselia first makes an appearance in D/P. After defeating the Champion, the player can go to Canalave City, and Sailor Eldritch (who let the player travel to Iron Island) has a problem. His son has fallen into a deep sleep, and plagued by nightmares. His only chance of waking up is getting the Lunar Wing, an item on Fullmoon Island. Once you get there, Cresselia appears and gives the player the Lunar Wing. You can come back to Fullmoon Island after this side-quest is complete, and Cresselia is there. Once the player interacts with it, it will fly away. Just like Mesprit, it becomes a roaming Pokémon.
Once the player reaches Lentimas Town, they can go east to Reversal Mountain, and go south to reach the Strange House. A ghost will lead you to the top room, and in the center of the room, you will find the Lunar Wing. Once the player defeats the Champion, they can go to Marvelous Bridge, and near the end of the bridge (if you are coming from Nimbasa City, near the beginning if they are coming from Black City or White Forest) and a text box will say that the Lunar Wing has started to shine, and giving you the option to hold it up. If you say yes, you will hear Cresselia's cry, and she will appear.
Cresselia made an appearance in Super Smash Bros. Brawl as seen in the background of the stage Spear Pillar, Palkia and Dialga also appear there. To attack, she will release a lunar "boomerang" that flies around the stage, bringing damage to the players it hits.