Celebi is the star of the 4th movie, and plays an important role in the 13th movie. It’s a cute event legendary, like Mew, Jirachi, and Shaymin. I find it kind of funny-looking; its arms look too long for its body.
Celebi, being a legendary Pokemon, has very high base stats (600). However, its type combination has one of the most weaknesses, including a 4x weakness to Bug.
Sources have confirmed some of the details about the free Celebi. It will be level 10 upon download. It will also come with Recover, Heal Bell and Safeguard moves, as well as a new move called Hold back, which is similar to a False Swipe.