Particles appear around the Wither Storm when it goes into the next Phase, so that it doesn't just seem as if mass just blips into existence. (Sorry idk how to describe it better)

What do you mean exactly? it already has particles around it, but we have plans to make that less obvious currently

Probably new particles that spawn upon evolving.

Ye

What I mean is that the Wither Storm is covered in particles when transforming into the next phase.

For a smoother transition

I don't think the particles existence would make much sense. Besides, we have some stuff coming that will help with the transition a bit.