In Baldur's Gate 3, you will encounter a series of interactions that will change the course of your adventure. Likewise, once you reach the end of the game, you will have to make the final decision of whether to destroy or control the Elder Brain. This is considered one of the most difficult decisions in the game, as it has the power to completely change the ending.
What Happens When You Dominate the Elder Brain?
While there is no right or wrong way to end BG3, they both have very different outcomes. To help you understand which option to select, here is a detailed walkthrough that will give you an idea of both scenarios before you can make your final judgment and choose your ending.
If you choose to destroy the Elder Brain, you are making the morally right and heroic decision. You can prevent the Mind Flayer threat and protect the people. Once you select the option "Go ahead, tell the brain to destroy all the tadpoles and then itself", the Elder Brain will start to malfunction and eventually disappear into the sea at the edge of Baldur's Gate.
As for the Mind Flayers, they also start crashing. The people defending the city also start attacking all the Mind Flayers, so that they are completely destroyed. In addition, all the people whose brains are infected by the Illithid parasite are cured.
