THIS IS NOT MY FINAL SUBMISSION! This is some reasoning.
And now, my prevos' story:
My bronze caterpillar is a happy, friendly, playful baby. Its protective plating sheds tiny particles so much that it can use Shield Dust. Its antennae can read the emotions of others, and its presence can comfort anyone.
As my caterpillar evolves, it turns from bronze to silver, and its psychic powers are enhanced considerably. It can now levitate a few feet from the ground, and, employing its own psychic-magnetic field, it can control the four pieces of its sloughed-off armor as it would a part of its body. They serve as its legs, since its real ones are now vestigial, and it also uses their sharp points in combat. It can also "feel" the emotions and thoughts of nearby humans and Pokemon, and people near it feel a sort of otherworldly presence.
When it evolves into Aurumoth, the last of its plating falls off and turns gold, its body floats upright, and it is able to fly, and do whatever else Aurumoth does. I have also slightly deviated from the traditional larva-pupa-moth chain.