1 Origin and theme

Pick or roll for the artifact's origin, the people who made it or the power to whom it's most closely tied (the Stone Lords, the Fae, the Things Below, etc.).

If you already know where the artifact came from, just pick. If a few different origins seem likely, either choose one for now (and feel free to change your mind later) or pick between them randomly.

Each of the possible origins in Book II has a table of related themes. Pick from or roll on the appropriate theme table. Allow the theme(s) to inform everything else about the artifact.

Looking at the origins table, "the Green Lords" seems like the obvious choice. I roll on the Green Lords' themes table and get a 2, "Plants and growing things, grandiose and/or unusual."