I have finally decided to reroll to my druid after years and have been using Lemix to unlock the bear and cat skins (never played legion through shadowlands). My question is, once I have the brown Moonspirit and brown guardian of the glade unlocked, can my main proceed to unlock the other forms, like the one that requires 200 world quest, or the BfA ones, or do I have to get the artifact on my main as well?
Yes. Although some might be easier in remix.
Originally, it was all about the artifact weapon and you couldn’t even use the forms without equipping it. But in more recent expansions, they changed the rules so you didn’t need to weapon anymore.
Some of the Skins require the Toon completing the Achievement for the different Color skins, to have the Base Artifact for that appearance unlocked. Remember that if you plan on Changing Mains again and still want need Skins.
But Once unlocked they should be account wide.