Reflection. Whether you're the max level allowed with stacked gear or running a new file or lvl 1. Reflection at the start of most fights will give you a huge advantage. A successful reflection will deplete boss stamina by half and depending on the build used, can then be depleted by your combos which will lead to a stun to more combos to brutal attack. And also try to use Reflection throughout the fights as well. Just remember which attacks you can not reflect. I do not recommend reflection for Aratra, Bellerian, Trokka at the start of the fight, and Hismar. And for anyone doing 3-phase Ozma, Your damage does not matter on the Third Phase. You want to deplete his stamina bar and then brutal attack as quick as possible 3 times and win. If a brutal attack depleted his life equal to the damage you dealt that would be different but every brutal only deals a third of permanent damage and has to be done 3 times.

For Ozma 3-phase, it is faster to just deplete his life bar normally than to brutal attack as a Brutal is actually slower overall.