If you received Scoundrel from the Pumpkin Patch, but did not get the achievement, please file a ticket and a staff member can verify and get the achievement for you. You do not need to provide a screenshot.
Please DO NOT file multiple tickets on the same topic. There may be other users ahead of you, so please be patient, and we'll respond to you as soon as we can.
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Keith should have fixed the achievement around noon on October 30th, so everyone should automatically receive the achievement after finding Scoundrel now.
I was trying to test the achievement to see if it would automatically go through, but I still haven't found Scoundrel. I'm glad someone confirmed they received it :D
[edit]Confirmed achievement is working:
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If you found Scoundrel before the problem was fixed on October 30th and did not receive the achievement, please fill out a ticket.