Matryoshka Shell Legendary Chest

So I found my way into a thing and after 6 or 7 bosses I got this:

 

Oh yeah same, I almost died from it :O

 

Where can you find this?

 

Jungle village, upon entering, on the left side in a cave. A guard is standing in front of the cave, uhhh and behind a bookshelf. That's the best directions I can give. Rip

 

I suppose a spoiler tag is in order, not sure how to add one.

The last boss (little white guy) was kind of derpy, the one before him was evil. Well made dungeon thing, I liked it....might be more there.

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ok sure

 

is it a boss altar????? i need this chestplate now lol

 

The powder slots tho