Terror Forged Mask quest and inny neck quest / mechanics

[Telemakus]

Hello!

What level is the earliest conceivable that one could begin the terror forged mask, assuming one is willing to even wait around in a zone until a specific mob gets killed?

At what level does the terror forge mask become useless (everything will resist)? Does that even happen? I'm wondering about the inny necklace as well in this regard.

Thank you!