Black Blood Sentinel

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, unarmed attack, or grapple against the attacking creature.
• 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  trigger *Reckless Defense (black blood required) except it is to defend your allies instead of yourself.
• *Reckless defense

  You raise your arm to block any physical attack, taking damage. If it would render you or your ally unconscious, this renders your arm useless (or gone) until regenerated.