Stardust can be collected by a druuvai over the course of their life. The more stardust a druuvai collects, the more powerful they become. Their magic gains specializations and focuses, and their traits can even evolve beyond their original appearance. When a druuvai gains more stardust than they can hold, some solidifies into more scales, horns, or even mutation traits. Some druuvai become taller, while some gain more potent magic.
Put simply, royal druuvai have more stardust than common druuvai, whereas mutation druuvai have an extreme abundance of it.