When you hit a creature with an opportunity attack, the creature's speed becomes 0 for the rest of the turn. The creature cannot be larger than one size above you, or you must have at least as much strength as the target.
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.
Great Weapon Master:
On your turn, when you score a critical hit with a melee weapon or reduce a creature to 0 hit points with one, you can make one melee weapon attack as a bonus action.
Whenever you score a critical hit with a heavy weapon that you are proficient with, double your weapon damage dice to the purpose of calculating the crit damage.
Elven Accuracy:
Any race can use this. You have uncanny aim with attacks that rely on precision rather than brute force.
Increase your Dexterity, Intelligence, Wisdom, or Charisma by 1, to a maximum of 20.
Whenever you are stealth and have advantage on an attack roll using Dexterity, Intelligence, Wisdom, or Charisma, you can reroll one of the dice once.