Short answer, no, its working as intended. It can only be triggered once per round.
Why is polearm Master and Sentinel good?
As you mentioned, Polearm Master lets you make an Opportunity attack as someone enters your reach; Sentinel lets you drop an enemy’s speed to 0. This also applies while they’re still 10′ away from you, meaning that unless they have a reach weapon, they can’t then make a melee attack against you.
Is Sentinel a bonus action?
Sentinel relies on this action/bonus action being done. If it is not performed, but instead you just do not provoke attacks or opportunity due to any other reason other than “Disengage” then Sentinel does not come into play. Clockwork DM. Gamer.
What’s the difference between Sentinel and polearm Master?
As you mentioned, Polearm Master lets you make an Opportunity attack as someone enters your reach; Sentinel lets you drop an enemy’s speed to 0. This also applies while they’re still 10′ away from you, meaning that unless they have a reach weapon, they can’t then make a melee attack against you. So, you may say to yourself:
Is the polearm Master unbeatable in a duel?
So if an enemy aproaches, you hit it with the opportunity attack from Polearm Master, and because of Sentinel it is now stopped 10 feet away from you. They can not hit you, you hit them on your turn and move back 5 feet. Repeat at will. Is this unbeatable in a duel? Am I not seeing something?
What are the benefits of the polearm Master?
One of the benefits of the Polearm Master feat (PHB, p. 168) is: While you are wielding a glaive, halberd, pike, or quarterstaff, other creatures provoke an opportunity attack from you when they enter your reach. One of the benefits of the Sentinel feat (PHB, p. 169-170) is:
When do you use polearm master on halberd?
The relevant portion of the Polearm Master feat says it works when you are using “a glaive, halberd, or quarterstaff”, and the effect is ” a melee attack with the opposite end of the weapon. This attack uses the same ability modifier as the primary attack.
