Mother Brain (Metroid)

Metroid
Mother Brain is the final boss in the game. You fight her in Tourian at the bottom of Planet Zebes. Mother Brain is incased in a glass case. Before Samus could defeat it, she would have to break open the glass that covers it. Preceding that she'd have to traverse through a sequence of traps that would put her jumping, dodging and shooting skills to the test. After Samus breaks the glass case, she must shoot missles at it to defeat it.

Its main form of attack is shooting out lasers via its single eye. It is a challenge to dodge on the account that 1. Samus is standing on a single pedestal, and on both sides of it is lava, 2. There are on coming projectiles, and 3. The laser is rapidly shot out.

Metroid Zero Mission
In this remake of the original Metroid, the fight wiht Mother Brain occurs mostly the same. However, she is not the final boss as Samus's ship is gunned down leaving Zebes. She must explore the Space Pirate Mothership and defeat a robot based off of Ridley.

Super Metroid
Mother Brain is also the final boss in Super Metroid. Samus first fights her the same way as in the original game. However, after it is defeated, it returns in a large robotic body. Samus attacks her by shooting missles at Mother Brain's head/brain. Towards the end of the fight, Mother Brain uses an attack that gravely damages Samus. The baby Metroid that thinks Samus is its mother from SR388 she saves at the end of Metroid II: Return of Samus comes and begins attacking Mother Brain. It dies, but not before giving Samus the energy it sucks from Mother Brain. Samus receives the Hyper Beam, which she then uses to defeat Mother Brain for good, from this.

Trivia

 * Mother Brain seems to look like Aurora Unit 313, who is a final boss of Metroid Prime 3: Corruption. In the Metroid Prime 3 Preview Channel, one of the videos shows the Auroa Unit in a setting very similar to the final boss level of Metroid.