Have you killed Balrog?

Sry I can't update you with useful drops cause most my runs were with you anyway.

As for how to turn your leathers in, I'm not sure you're hinting to "where" or "how many a time". If you meant where, they recently added another path below the Insignificant Being, you can't drop down to him though since the rope has been taken away. Instead, make a detour to the previous map, drop down to the bottom right and search for a hidden portal in the bone hill (bottom platform).

As for how, probably 30% scrolls for 2dex sounds reasonable. I wouldn't risk all 6 slots just to hope a Twilight will land.

How many at a time.