Jirachi, Mew, and Celebi will appear 1/493 of the time individually.
A Wish Pokémon. It's said to awaken for seven days every thousand years, with the ability to grant any wish asked of it. It is truly a Pokémon of which dreams are made. In combat it uses its wish power to attack. Its attack Doom Desire, which causes light to rain down from the heavens to do tremendous damage, is especially powerful.
"You've encountered JIRACHI for the first time! Make a wish!"