Brawler Joy of battle - Damage contradicting tooltip

[CasualActual]

Tooltip says -incoming damage, then goes on to say stacking damage buff. Which is it?

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[Antophant]

Joy of Battle does both, for 15 seconds you gain a -20% inc dmg buff and also during those 15 seconds you can hit mobs to gain a stacking melee damage% buff up to 20%(28-31%) at 10 stacks that lasts 20 seconds.