I’ve done the Strange Mushroom Ring encounter twice, as well as killing Taja the Tidehowler twice. None of the kills contributed towards the achievement.
Still nothing for Taja the Tidehowleer. Killed on a character at level 65 and no progress on the achievement
IT WORKS NOW. PROGRESS COUNTS ON BOTH TAJA THE TIDEHOWLER AND THE STRANGE MUSHROOM RING (at least at level 65). PRAISE BLIZZARD