Help me Understand the Nightmare Tatters

https://preview.redd.it/fqb01dwlsytg1.png?width=676&format=png&auto=webp&s=607f644a49e98f8b061274865f5ca2173cc873c7

Me and my friend are playing Nightmare mode to get tatters, but when we got 84 it just cyclend back to going from zero with the excess.
I don't understand how the percentage bar is working. is this just our clan? is this a whole community thing?
what does collecting 84 tatters even do? not much is explained here.