Each battle that you win will yield experience for each pet that participated. However, deceased companions will not receive any experience (so make an effort to keep them alive by swaping in a different pet). Experience gains are based on your pet's level compared to the wild pet. Defeating a higher level opponent will grant more experience than a much lower level one, but be ready for a tough fight!
Things like the Fishing training book from Booty Bay and the First Aid book from Stromgarde (A) and Brackenwall (H) will fetch a very good price, but even the less rare items like Undermine Clam Chowder recipe (from Steamwheedle Port, Tanaris) can sell well. The Limited Supply routes in capital cities in Legion is still the same route and vendors as back in vanilla. Become a Patreon to The Gold Queen and see the limited supply routes for IF, SW, Darn, Org, UC, and TB, as well as the Booty Bay special, in videos as part of the gold guide I’m still crafting.
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Unlocking the Lightforged will require you to complete the aforementioned Argus storylines and earn the “You Are Now Prepared” achievement. In addition, you’ll have to earn Exalted status with the Army of Light. As with the Argussian Reach, this one could take a couple of weeks, as it is time-gated. However, the main story quests should help you at least reach Friendly status with the Army of Light.