Consumed by Shadows:
From Sneak: Active attack. Enemy must make a Will save versus 20 + highest ability score + Assassinate or be beset by your shadow. Enemies affected have their Armor Class set to 0 for 5 seconds, and when they are hit, they take a stack of Vulnerability. Cooldown: 30 seconds. Note: This ability requires the character to have the Stealth feat active ("in stealth") to use it.
vs
Weird: The Weird spell is added to your spellbook as a level 9 spell if you are a Cleric, Sorcerer, Druid, Wizard, or Favored Soul, or a level 6 spell if you are an Artificer, Alchemist, Bard, or Warlock. Requires the ability to cast spells of those levels.
Weird: A targeted foe and all nearby enemies are subject to a Phantasmal Killer effect, with a DC20 + highest of INT/WIS/CHA mod + Illusion spell bonuses to prevent the death.
Nobody takes the former, almost every DC caster take the latter. Because the former is too weak, the latter is too strong.
Shadow Mastery: Epic Moment: Dissolve into a whorl of shadow, leaving your corporeal form behind. While in this form, you are considered Sneaking and Invisible regardless of what you do. You also gain 3d6 Sneak Attack Dice, 50% Incorporeality, as well as the effects your Epic Strike as if they had been fully trained and upgraded. When non-boss enemies miss you in this state, they are slain by their fear, automatically taking a Phantasmal Killer effect with no save. Duration: 20 seconds. Cooldown: 5 minutes.
So, you need to expose yourself to danger to proc this one when sometimes JUST 1 HIT means death on R10. It even has an internal cooldown, you can't have multiple proc at the same time. It has so low uptime / cooldown ratio, too, when you consider its low power.
Why do you hate sneaky types SO MUCH?