Some things about polearm mastery that are correct per the rules as written that I have seen people have issue with but in all honestly are not that big of a deal.- Both the normal attack and the bonus d4 attack have reach.
- Both the normal attack and the bonus d4 attack add str modifier to damage.
- Both the normal attack and the bonus d4 attack are made with a 2-handed weapon, so things like great weapon master -5/+10 and great weapon fighting style (re rolling 1's and 2's on damage dice) apply to the d4 bonus attack.
- You can take your bonus attack before the attack action itself, almost all bonus actions work like this you can take it at any point in your turn as soon as you commit to taking the triggering action.
- Anything applying bonus to hit or damage applies to the bonus action d4 attack so magic item modifiers or buff spells, stuff like that.
Up until now I had never seen anyone trying to balance out the feat by saying you wouldn't get your proficiency bonus to attack on the bonus d4 attack, of course you do if you are proficient with the polearm.
Now remember you are limited to one bonus action on your turn, no matter the number of attacks you get with the multi-attack class feature, I have seen people make the mistake of letting a 5th level fighter get a bonus attack twice because he makes two attacks with main end of the weapon.
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