So with the Cleave weapon mastery it says you get an extra attack against an enemy in 5ft after you hit and it says you don't add your ability mod to this extra attack.
With Great Weapon Master you add your Proficiency Bonus when attacking with a Great Weapon, would that damage be added to the extra attack from Cleave?
Yes, if the attack is part of your Attack Action. The only thing you don't add on the Cleave extra attack is your ability score modifier.
The only other condition for Great Weapon Master is that the attack is part of your Attack Action. While Cleave is once per turn, it doesn't have to be part of the Attack Action. If you make a Cleave attack as part of an Opportunity Attack, it will not get the bonus from Great Weapon Master.
It will also not get the bonus if you make an Bonus Action attack as part of Polearm Master.
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So with the Cleave weapon mastery it says you get an extra attack against an enemy in 5ft after you hit and it says you don't add your ability mod to this extra attack.
With Great Weapon Master you add your Proficiency Bonus when attacking with a Great Weapon, would that damage be added to the extra attack from Cleave?
Yes, if the attack is part of your Attack Action. The only thing you don't add on the Cleave extra attack is your ability score modifier.
The only other condition for Great Weapon Master is that the attack is part of your Attack Action. While Cleave is once per turn, it doesn't have to be part of the Attack Action. If you make a Cleave attack as part of an Opportunity Attack, it will not get the bonus from Great Weapon Master.
It will also not get the bonus if you make an Bonus Action attack as part of Polearm Master.
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Ahh thanks for the answer, that extra bit about the AoO is very helpful too.