We have a full batraal fight video with kill at 35+ minutes, and the ending clip is what I posted so far.

In that clip you can see there is the missing chest, and also see that the other chests (besides batraal golden chest) are missing. By skipping all the other stuff in dungeon, it saves the time needed to get to the Batraal quickly.
Now you just have to kill batraal quickly! Unfortunately, at this moment, we want to keep our fight strategy a little secret which is why we don't post that just yet, but it is already uploaded ready to be viewed at some point, time dated.
One thing tho, we have posted pictures and videos confirming the chest does exist. So far I have not seen any others post that

including the JP shells that have killed in time as well.
the JP linkshell said kill time, and we have said kill time
I wish you all luck in figuring out a good fast kill strategy. That is part of the excitement and fun in this game!
