Masked Soliloquy

If you are going for multiple mask runs these are the order of difficulty in my opinion:
Easiest - [item=174081] - when you are below 50% sanity you will spawn an aberration every 1-2 minutes that will attack you and keep you in combat until you kill it. At 460 ilvl it has around 180k health.
Easy - [item=174083] - causes small void pools to appear behind you as you run and stepping in them will drain sanity.
Medium - [item=174079] - you are now affected by 2 afflixes in every area instead of 1. The difficulty of this one varies from week to week as the affixes and type of vision change.
Harder - [item=174082] - all damage by enemies that drains sanity drains 5 times more sanity.
Hardest - [item=174080] - reduces your Sanity by 50%.

You obtain the masks by doing the following:
[item=174080] is obtained from the end chest after completing all 5 objectives in a single Horrific Vision (both corrupted areas, both lost areas and Thrall or Alleria).
[item=174083] is obtained from the end chest after completing the Valley of Wisdom lost area in a Horrific Vision of Orgrimmar with any other Faceless Mask active (you do not need to defeat Thrall).
[item=174082] is obtained from the end chest after completing the Valley of Honor lost area in a Horrific Vision of Orgrimmar with any other Faceless Mask active (you do not need to defeat Thrall).
[item=174079] is obtained from the end chest after completing the Old Town lost area in a Horrific Vision of Stormwind with any other Faceless Mask active (you do not need to defeat Alleria).
[item=174081] is obtained from the end chest after completing the Mage Tower lost area in a Horrific Vision of Stormwind with any other Faceless Mask active (you do not need to defeat Alleria).

Tooltip reads "Increases Sanity damage from creatures by 400%". Some maths for you maledin. If you get hit by an ability that drains 1 sanity, 100% increase is 2 sanity, 200% increase is 3 sanity, 300% increase is 4 sanity, 400% increase is 5 sanity. 5 is 5 x 1 so it's 5 times more sanity.

Likewise, Faceless Mask of the Daredevil similarly gets easier as we gain more sanity resistance, just not as dramatically as the Long Night. Take Magister Umbric's Entropic Missiles ability, which drains 15 sanity per sec for 3 seconds, before resistance. With Daredevil on, it'd drain 30 sanity at rank 10 (50%), whereas it'd only drain 12/sec at rank 15 (80%)—equivalent to its sanity drain if your cloak was at ranks 1 & 2 (20%) with no mask! Essentially our increased sanity resistance is a continuous soft nerf on visions, and especially with the difficulty of certain masks.