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Very easy, and little RNG involved. Start the game as the Goblin Shaman, and just run around until you encounter an enemy with Goblin or Hobgoblin in its name. Instead of fighting it you get the option to Spellbind it. Click that button and it'll immediately go into your inventory as a follower. You'll see you have a new option to get a spell, but don't use it as you'll sacrifice your Spellbound goblin for that. Instead just run to the Sentinel and try crossing into the Middle Region. Lose to the Sentinel and you'll get the option of sacrificing your Spellbound goblin, which will unlock the achievement!