Trophy Collector (5e Feat)
From D&D Wiki
You can now collect 1 trophies for every enemy you kill which is greater than CR 1/4(you must be the one dealing the killing blow) the more trophies you collect, the stronger you become as well.
At 10 trophies : +1 to attack rolls
At 20 trophies : +1 to damage rolls
At 30 trophies : +5 hit points
At 50 trophies : +2 to attack rolls and +2 damage rolls