Its your Motherbrain and she's mad that you didn't wash the dishes!
Motherbrain is back for a new purpose and a new goal. She's been infected by the seed and its up to you to purify her. Motherbrain is pretty much the same as Dulk Fakis in pretty much everything, with a few minor differences.
Her mainly annoying action is to put shields up. During this time if your in a large party, this won't be much of a problem. Your party can just keep blasting at her sheilds while someone is there to heal you. However in a 1-2 person party this will be problematic as most of your attacks hit 0. During this time its best to wait for her arms to come down, back away before they slam on top of you, then attack her arms directly. When her arms moves towards you, face forward and try not to turn your back against it. We'll explain in more detail later on why you should do that.
Motherbrain tries out new relaxing breathing techniques
Her other attack is the blueish purple gas that comes up most of the time when she has her sheilds up. You should again face forward and keep running forward when this gas pushes you back.
When her shields are down, you have a limited time to attack at her face. Listen for the vocal and sound effect cues that tell you when she's about to put her machine gun and blast you to peices. Its easily avoidable if you pay attention to a white ring on the ground. However if your constantly dodging her machine gun attacks you won't have any time to even hit her.
So why should you face forward during her attack? Leo yells, "From Behind!" for a reason. If your back is facing her arm, she will have a higher chance of critical damage against you. If you face forward, you will have a higher chance of dodging her attacks, thus you'll be able to do the Just Counter. For her arm, I would suggest to stay away from it when she's about to push you back since you won't be dodging her attacks all the time, but if you get stuck in the situation where your pressed against her arms, just face forward. For her purple gas, I always recommend staying forward because this is her most easily dodgeable attack.
