Just bring Wyll, Eldritch Blast kills them a lot faster than any other character as they seem to be resistant to arrows and Gale's atrocious cantrips.
Previously I was able to pickpocket Nettie's crown that Halsin mentions, which also gives you +1 nature, but it seems like this latest patch removed that as it's no longer in her pickpocket inventory, so you can't grab the crown to go the other way around.
