Anchor Howl

You can start Anchor Howl, alerting all enemies within 60ft. On your turn, you can take an action to activate the following ability: as a reaction within the area of effect a 15 ft circle centered around the user, within line of sight, if you have the appropriate movement speed which persists from your turn, you can make one opportunity attack against a creature. If the opportunity attack is against a creature attacking an ally, the attack is interrupted if you succeed. Unless the creature lands a critical hit, the intended target takes half damage. The ability lasts one minute or until you use 4 ability-based opportunity attacks. These Anchoring Opportunity Attacks take the place of 'Opportunity Attacks'. 

(Creatures within the 15ft AOE provoke Anchoring opportunity attacks when leaving the AOE, attacking an Ally, or as per normal upon leaving melee range.)
(The 'Anchor Howl' ability that grants these Anchoring Strikes lasts one minute, or until you use 4 ability-based opportunity attacks.)

(Caster may pick one enemy not to affect.)
(2 use per Long Rest)
(Permanent -2 damage debuff {First Use, Non-Stacking})