Shalazam

Yes, it opens the Weathered Treasure Chest - see it on [url=https://shalazam.info/maps/1?q=weathered+treasure+chest&zoom=8&x=1741&y=153]the map[/url] We've also just created a new [url=https://shalazam.info/item_collections/246-weathered-treasure-chest]Item Collection[/url] to show you what can drop from this chest.

Is this key just to open a chest inside NFC?

If your facing the locked gate leading to Saruth, directly behind is another room with 2 statues that come to life, that wall is a false wall you can walk through, beware soon as you walk it there is a long corridor filled with poison gas, so far only the pally we had could make it to the end without death. There is a clear area with key to gate

The debuff is called Weakened Frame, and I'm guessing it says "Cannot be affected by Weave the Wind" which is a Druid spell that does almost the same thing. Because when I cast Weave the Wind on my Druid, I get the Weakened Frame debuff that says "Cannot be affected by Interlocking Stones" which is what led me here to find out what Interlocking Stones was, lol.

Apparently this key is for chests in The Crypt, opened a chest and this key disappeared. Got a nice one hand sword, will post stats after patch, lvl 19 req.