The nightmare lords of the forgotten depths typically grant mortals power for one of two reasons: some use mortals to weaken the surface world and thus prepare for an eventual takeover and others use mortals as proxies in the almost ceaseless wars they wage on each other.

Level 1: Dark Pact Reward

As a dark pact hexblade, you learn to move like the skittering bugs and lizards of the underground. This swiftness and ability to come from an unexpected direction makes your attacks more lethal than others might suspect.

Benefit: You gain a bonus to the damage rolls of your warlock and warlock paragon path powers equal to your Dexterity modifier. The bonus increases to 2 + your Dexterity modifier at 5th level, 4 + your Dexterity modifier at 15th level, and 6 + your Dexterity modifier at 25th level. At 9th level, you also gain this bonus to the damage rolls of creatures you summon with summon warlock’s ally…

Level 1: Dark Pact Boon

The great powers of the underworld have magic that weakens foes, like noxious gases that corrode opponents’ powers as acid dissolves rock. You can draw on the life of a dying foe to spread that weakness to others.

Benefit: You gain the soul blight power.

Soul Blight (Warlock Utility)
As one rival falls, weakness spreads to its allies.
At-Will • Arcane
Free Action                        Close burst 5
Target: One enemy in burst.
Trigger: You reduce an enemy to 0 hp, or an enemy adjacent to you drops to 0 hp.
Effect: The target creature is weakened until the end of its next turn.
Special: You can only use this power once per round.

Level 1: Dark Pact Weapon

The blade of tormenting night is a gift from twisted subterranean lords. Made of a black, mirror-like metal, it is razor-sharp with curved and jagged edges, like chiseled obsidian. Short and quick, it scuttles through enemies’ defenses like a centipede darting underneath a log, finding weak points before striking home. Channels in the glassy metal seem to carry the blood of the Underdark, corrosive and sickly green. Through it, you can make the following two attacks.

Blade of Tormenting Night (Warlock Item)
Black and glassy, this blade drips a fluid that stains skin—what skin it leaves behind, at any rate.
Weapon Category: One-handed military weapon.
Weapon Group: Light blade.
Proficiency Bonus: +3.
Damage: 2d4.

Vitriolic Slash (Warlock Attack)
You dart in and slice your foe. A greenish liquid splashes off your sword to agonize nearby enemies.
At-Will • Acid, Arcane, Implement, Weapon
Standard Action                               Melee
Requirement: You must use this power with your blade of tormenting night.
Target: One creature.
Attack: Charisma vs. AC.
Hit: 1[W] + Charisma modifier acid damage, and each enemy adjacent to you other than the target takes 2 acid damage. If no other enemies are adjacent to you, the target takes an additional 4 acid damage.
Level 21: 2[W] + Charisma modifier acid damage, and each enemy adjacent to you other than the target takes 4 acid damage. If no other enemies are adjacent to you, the target takes an additional 8 acid damage.
Special: This power can be used as a melee basic attack.

Debilitating Corrosion (Warlock Attack)
The open wound you leave on your opponent gives off a miasma that spreads to nearby allies.
Encounter • Acid, Arcane, Implement, Poison, Weapon
Standard Action                               Melee
Requirement: You must use this power with your blade of tormenting night.
Target: One creature.
Attack: Charisma vs. AC.
Hit: 2[W] + Charisma modifier acid and poison damage. At the beginning of its next turn, the target and all enemies adjacent to the target take acid and poison damage equal to the damage bonus from your Dark Pact Reward.
Level 13: 3[W] + Charisma modifier acid and poison damage.
Level 23: 4[W] + Charisma modifier acid and poison damage.