Level 3
Bump in the Night.
When target(s) of your necrotic spells cannot see you, suffer 1 wound to change the primary die roll to whatever you like (changing to the max value counts as a crit). AoE spells deal max damage instead.
Tainted by Darkness.
Your patron grants you the One with Shadow Greater Invocation. Your Shadow Minions become inky black imitations of you. Your Shadow Blast and minions cause you to become Invisible until you move or attack whenever they would crit.
Level 7
Shadow Stalker.
(Whilst invisible) Reach 8. Action: Teleport to a space in darkness or adjacent to a shadow minion. Remain Invisible until you move or attack.
Level 11
Blackout.
Action: Sacrifice a Shadow Minion. Envelope a 3x3 area in total darkness where the minion was until you attack. Creatures (excluding you and your minions) cannot see through this darkness, and become blinded whilst in this area.
Level 15
Darkness, My Old Friend.
Saving Throws triggered by spells cast while your target(s) cannot see you automatically fail.