Eldritch Smite
Source: Xanathar's Guide to Everything
Prerequisite: 5th level, Pact of the Blade feature

Once per turn when you hit a creature with your pact weapon, you can expend a warlock spell slot to deal an extra 1d8 force damage to the target, plus another 1d8 per level of the spell slot, and you can knock the target prone if it is Huge or smaller.


One with Shadows
Source: Player's Handbook
Prerequisite: 5th level

When you are in an area of dim light or darkness, you can use your action to become invisible until you move or take an action or a reaction.

Thirsting Blade
Source: Player's Handbook
Prerequisite: 5th level, Pact of the Blade feature

You can attack with your pact weapon twice, instead of once, whenever you take the Attack action on your turn.

FEATS:
Polearm Master
Source: Player's Handbook

You gain the following benefits:

When you take the Attack action and attack with only a glaive, halberd, quarterstaff, or spear, you can use a bonus action to make a melee attack with the opposite end of the weapon. This attack uses the same ability modifier as the primary attack. The weapon's damage die for this attack is a d4, and it deals bludgeoning damage.
While you are wielding a glaive, halberd, pike, quarterstaff, or spear, other creatures provoke an opportunity attack from you when they enter the reach you have with that weapon.

Sentinel
Source: Player's Handbook

You have mastered techniques to take advantage of every drop in any enemy's guard, gaining the following benefits.

When you hit a creature with an opportunity attack, the creature's speed becomes 0 for the rest of the turn.
Creatures provoke opportunity attacks from you even if they take the Disengage action before leaving your reach.
When a creature within 5 feet of you makes an attack against a target other than you (and that target doesn't have this feat), you can use your reaction to make a melee weapon attack against the attacking creature.