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Technically, it was untradeable even before BB.
It was only tradeable for a limited time.
Since now there's the dimensional crack, you don't have to go to Sleepywoods to participate in Astaroth PQ.

you don't even need the helmet anymore after BB. it was tradable THEN untradable BEFORE BB. BB just made it so you don't need it for the astoroth pq anymore.
U used to need it to pass this gas map, to the astoroth pq.

Its a item from a quest that you need for PQ, it was trade-able pre-bb but now its not tradeable.