The Way of the Slayer focuses on diving headfirst into combat,  proving the user's strength with inescapable grapples, crippling blows, and intimidating confidence. There is no order that follows the Way of the Slayer, and monks that follow this path are not righteous, calm, or peaceful in the slightest. A monk with Slayer techniques in their mind is blind to all power but their own, and constantly seeks to prove and test themselves. The ambition of a Slayer often leads to dangerous situations, which often only thrills the Slayer and further enthralls them into the trance of battle. A Slayer lives for the fight, loves the fight, and dies in the fight.

Slayer Soul

3rd-level Way of the Slayer feature

Your body is bolstered by the furious river of Ki that flows through you, granting you an unnatural aura of power.
You gain proficiency in the Athletics skill, and gain temporary hit points equal to your Martial Arts die each time you use a ki point.
On a bonus action, you may spend a ki point and attempt to make a single creature that can see or hear you frightened until the end of your next turn by forcing them to make a WIS save against your monk DC. 

Power Grip

3rd-level Way of the Slayer feature

Your fingers are inescapable, and press into your enemies like the grip of a dragon's jaws.

Whenever you succeed on a grapple check against a creature or you start your turn grappling it, it takes damage equal to your proficiency bonus. 

Broken-Toothed Grin

6th-level Way of the Slayer feature

The sweat, blood, and bruises of combat are what you live for. Nothing scares you anymore, and being pushed to your limit in a fight only serves as a chance to prove your strength against all odds.

You are immune to being Frightened. Whenever you fall below half of your maximum hit points, you roll one Martial Arts die and regain a number of ki points equal to the number rolled, and can make one more attack when you take the attack action on your next turn.
This effect may only trigger once per combat encounter, up to a maximum of 4 times per long rest.

Overwhelming Ki

11th-level Way of the Slayer feature

Every move, every hit, and every sway of your ki-infused fists is rooted in self-confidence, power, and cruelty. Those subjected to your might are left cowering and terrified, unable to retaliate against your great and powerful soul. Whenever you use at least 2 ki points in a turn, up to 2 creatures you are engaged with must make a WIS saving throw against your DC. On a failure, they are frightened of you until the end of your next turn. This ability may only trigger once per turn.

While a grappled creature is frightened of you, it cannot attempt to attack any target other than you or break the grapple for the duration of the condition.

Their Weakness is Your Strength

17th-level Way of the Slayer feature

You are a cruel monster in combat, drawing upon the fears and weaknesses of your foes to turn a fight even further into your own favor.

Every time you reduce a creature to 0 hit points, you regain 1d4 ki points.
You gain advantage on attacks against creatures that are frightened and grappled by you at the same time, and successful attacks on these targets deal an extra damage die of your chosen weapon's type.