FusionDex

Castyu fly up into heavy rainstorms, merrily twinkling their blue core in time with the rainfall. In the moments between the rain stopping and the clouds clearing, the sky sparkles with their lights in a dazzling array of pulsing lights.

It gathers with others in the night and makes its red core glow on and off with the twinkling stars. It alters its form depending on the weather.