Alright, so I got into the Rattkin Tree, despite only getting one short Gooda Vine... I had to use the trainer to teleport in, and then I opened the back door entrance up so I could leave and exit from ground level..

Question:

There's a building that is divided by a sort of latticework wall, with what appears to be a door inset, next to a plaque... I can't open that door for the life of me, and no use icon shows up... I imagine the chest inside holds the Helm of Serenity? How do I get in?

SPOILER:

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You have to get Marten's Idol from Marten's Bluff. The Shaman will be waiting for you there at the 6th Bough when you get back.

Cheers,
-Sazerac

Eeep.

Unfortunately, I had brought the idol back before I ever entered the Rattkin Tree.

I used the Key of Serenity to open the door to that house, but the latticework gate won't open... Bah.

Time to restart? It's beginning to sound like my game is massively fubar'd.

Have you already talked to the Shaman in the 7th bough (used the Zuzu petals and the Mystery Potion from Fuzzfas there?) He won't appear in the Rattkin tree until you've talked with him at the seventh bough.

The Seventh bough is the one that leads off from the Pagoda.

-Sazerac