It was pretty easy for me to obtain, i did it in 2 new games. First don't save anyone on the ship when it goes down. Get the to the elf that is hiding with the child and get her pouch through conversation.And turn in Stingtail to Griff, it always gives me the Villian Tag. In my Recent playthrough i got the villian tag on reapers coast, it unlocked while i was draining a ghost even though i already had the Hero Tag, so i am unsure how exactly i got it.
