The second ability of Polearm Master is “While you are wielding a glaive, halberd, pike, or quarterstaff, other creatures provoke an opportunity attack from you when they enter your reach.” This is even more powerful than a bonus action attack, this is a reaction attack. The ability to use a reaction is even more limited than a bonus action. Also, because this is an opportunity attack, there are a few more abilities that can trigger. Getting out of range and having a target move into or back into range is the key to using this ability consistently.
Take a look at the Sentinel feat. If you hit a target with an opportunity attack, the target’s speed drops to 0. Because Polearm Master allows an opportunity attack against a target entering threatened squares, a reach weapon has the potential to stop a target from even getting close enough to attack you in melee.
One of my first D&D characters of this edition was an Oath of Vengeance paladin. At 7th level, they gain the Relentless Avenger ability. When you hit with an opportunity attack, you can move up to half your speed. Add everything together and it becomes a game of keep away as you ground your target to a halt with opportunity attacks. Even at early levels, you can potentially make 3 attacks per combat round–Attack, bonus action, and reaction/opportunity attack–and reduce the risk of counter-attacks at the same time.
I have used this hack to very good measure as the party tank and I can recommend it as play-tested, not theory.
If you have a hack you would like to submit, please let us know in the comments below!
But… what do I know…?