This egg was only available in Egg Cave's Cash Shop Park for July 2015.
Sylvern eggs form during summer rain showers, not on the ground but up in the clouds. This is also the only time that you can acquire one of these eggs as they will float away to parts unknown after the rain is over. If you wish to obtain a Sylvern egg you need to get the help of something with wings that is not afraid to fly in the rain.
Sylverns spend most of their lives in the sky playing in the clouds. Only during rainstorms does a Sylvern come close to the ground and even then it will never actually land. Because Sylverns are seen so frequently flying about during the summer rains there are many stories that Sylverns can control the rain. However the SAR Center has discovered that there is no truth to the tales that Sylverns can control the rain. Sylverns have a connection to rain, that is certain, but they can not control it.