In one of my tried damaging Mileena in Mortal Kombat X Invasion Boss, I was able to do 113 damage and survive 30 seconds. When you able to do so, it will say “Excellent” and show the text: “You have dealt a blow to the Invasion Boss”. This is unlike most of the times where it says “You were annihilated by the Invasion Boss”.
Mileena was able to do Brutality at the end, but I think it didn’t count as the match was already over (lucky me) 🙂
Take a look at the Invasion Boss gameplay video in Mortal Kombat X.