Slayer

Unfazed by the multiple fatal blows delivered by the horde of lesser demons, the half-orc continues to mow them down with his battle-ax.

As the Goliath battles the way through the mob of goblins their weapon becomes too slick with blood to hold anymore so he grabs one of the slain goblin’s clubs and resumes.

When the usually stoic human hears about the monster that’s pillaging the nearby town he remembers back to the moment that made him who he is today and jolts up to ask about information about the one they’ve been tracking all these years.

Just a small first attempt as a sub-class, feedback appreciated. 

Massacre Meter

As you track, murder, or do actions that pertain to your favored enemy you gain points that affect your rolls. These reset every 8 hours after the first point is gained.

Sense of Bloodlust

When you use this ability, if you're within the specified range of your favored enemy you can detect where they are and how many there are, you also can get a vague representation of their strength relative to yours. This counts towards your massacre meter and can be used every 3 minutes.

Expanding Rage

Your anger has expanded to where the effects granted by the Favored Enemy feature twice to one of your two favored enemies. You can apply this feature again to one of your three favored enemies when you reach level 15, including the one you already applied it to, to make it a max of 3.

Targeted Massacre

At 11th level, you gain the ability to use all your points in your massacre meter as a bonus in a battle, however, you may only attack one targeted enemy, and after the enemy is killed all subclass features are disabled for 24 hours, the Massacre Meter is disabled for 48 hours, and you are sent to level 3 of exhaustion. However, while using targeted massacre you cannot be paralyzed, charmed, frightened, or petrified, and things have disadvantages on grappling, restraining, or stunning you.

Slaying

If a favored enemy is under 20 hp you can take an action to instantly kill it.