Mother Brain

Mother Brain is one of the recurring main antagonists in the Metroid universe, alsongside Kraid and Ridley. Being an organic, living brain, it took over the Planet Zebes and therefore got to be the final boss of Metroid and Samus Arans main enemy in several games. It then sent out several creatures to stop Samus, including Ridley, Kraid, the Metroids and even the Chozo Statues. Luxkly, her plan failed.

In Super Smash Bros. Melee
It appears in the background of Brinstar, making the acid level raise and fall with earthquakes.