What? Mother Brain you say?
Of course! The main antagonist from the original Metroid, and Super Metroid too, would hardly be a playable character in any fighting game, but she would be a perfect boss for Subspace Emissary.
If you don't know what Mother Brain is, she's supposed to be an Artificial Intelligence in charge of Planet Zebes' defenses (it isn't clear if she's the leader of the Space Pirates or not). She was apparently created by the Chozo. In its latest appearances she looks like an one eyed Brain (duh) protected in a resistant glass container. She is always surrounded by defense systems and a pool of deadly liquid.
Mother Brain, wit the glass case broken:
The battle would go somewhat like this: You have to proceed through Mother brain's chamber, breaking life support tubes and dodging the Acid and Laser Turrets planted along the way.
When you finally reach Mother Brain, you have to attack the glass protecting her. Characters with projectiles would have an easier time doing this. Upon this point, MB doesn't do anything and relies on Laser Turrets that push you in the Acid. When you break the glass, you can start damaging Mother Brain, but she opens her Eye and begins attacking herself with a powerful energy beam; you can see her charging this attack.
When you defeat MB, its chamber blows up, and a timer starts. As usual, she has SET YOU UP THE BOMB!!! (Zero Wing Reference). You have to escape in a fashion similar to the metroid stage in melee's Adventure Mode.
Or alternatively, if you can defeat her fast enough in higher difficulty settings...
Mother Brain's Pod explodes and she falls to the ground. It appears to be dead for a few seconds, but the whole room starts shaking; seconds later, it emerges from the ground, with a powerful new battle body!
MB's Body from Super Metroid:
She's humongous. Mother Brain can now walk and attack with its new limbs. Also, she can spit explosive orbs, uses a flamethrower from his arms, and when it's close to defeat, will start using its powerful Mindblast, shown in the picture. It's a lethal attack that will rack up your damage quickly. When you defeat this form, the time bomb will activate as described before and you'll have to escape. (This form of mother brain should only appear if you do well enough in normal or harder difficulty, between normal MB and the escape sequence)
So, that is how i think Mother Brain should appear in brawl, as a Boss only character. It could even be working with the Primid, either in an underground base or inside the Halberd itself.
Of course! The main antagonist from the original Metroid, and Super Metroid too, would hardly be a playable character in any fighting game, but she would be a perfect boss for Subspace Emissary.
If you don't know what Mother Brain is, she's supposed to be an Artificial Intelligence in charge of Planet Zebes' defenses (it isn't clear if she's the leader of the Space Pirates or not). She was apparently created by the Chozo. In its latest appearances she looks like an one eyed Brain (duh) protected in a resistant glass container. She is always surrounded by defense systems and a pool of deadly liquid.
Mother Brain, wit the glass case broken:

The battle would go somewhat like this: You have to proceed through Mother brain's chamber, breaking life support tubes and dodging the Acid and Laser Turrets planted along the way.
When you finally reach Mother Brain, you have to attack the glass protecting her. Characters with projectiles would have an easier time doing this. Upon this point, MB doesn't do anything and relies on Laser Turrets that push you in the Acid. When you break the glass, you can start damaging Mother Brain, but she opens her Eye and begins attacking herself with a powerful energy beam; you can see her charging this attack.
When you defeat MB, its chamber blows up, and a timer starts. As usual, she has SET YOU UP THE BOMB!!! (Zero Wing Reference). You have to escape in a fashion similar to the metroid stage in melee's Adventure Mode.
Or alternatively, if you can defeat her fast enough in higher difficulty settings...
Mother Brain's Pod explodes and she falls to the ground. It appears to be dead for a few seconds, but the whole room starts shaking; seconds later, it emerges from the ground, with a powerful new battle body!
MB's Body from Super Metroid:

She's humongous. Mother Brain can now walk and attack with its new limbs. Also, she can spit explosive orbs, uses a flamethrower from his arms, and when it's close to defeat, will start using its powerful Mindblast, shown in the picture. It's a lethal attack that will rack up your damage quickly. When you defeat this form, the time bomb will activate as described before and you'll have to escape. (This form of mother brain should only appear if you do well enough in normal or harder difficulty, between normal MB and the escape sequence)
So, that is how i think Mother Brain should appear in brawl, as a Boss only character. It could even be working with the Primid, either in an underground base or inside the Halberd itself.