Adventure Mode: The Subspace Emissary

Adventure Mode: The Subspace Emissary (亜空の使者) is the Adventure mode in Super Smash Bros. Brawl. It centers around the playable fighters and their intertwining struggles against the Subspace Army. Among these characters is Samus Aran, who starts out as Zero Suit Samus before regaining her Power Suit.

Samus Aran's role
Samus Aran's involvement begins when she infiltrates the Research Facility on the Isle of Ancients as Zero Suit Samus. After working her way through part of the facility and defeating the various R.O.B. sentries she encountered along the way, she discovers a trapped Pikachu that is being drained of its electricity; once Samus frees the Pikachu, it teams up with her for much of the remainder of The Subspace Emissary. After defeating the R.O.B. sentries that responded to the alarms set off by Pikachu's release, Samus and Pikachu make their way further into the Research Facility, where they eventually find a screen displaying Samus's Power Suit that is being held elsewhere in the facility, presumably being studied. Zero Suit Samus and Pikachu make their way to the chamber where the Power Suit is being held; before Samus can recover it, however, two darker versions of her Power Suit attack the duo. After defeating the Copied Power Suits, Samus dons her Power Suit; beyond this point, it seems to be impossible to play as Zero Suit Samus until The Great Maze, where she can be selected by highlighting Samus and pressing the - button on the Wii Remote or the Z button on a Wii Remote with a Nunchuck attachment. With her Power Suit recovered, Samus continues working her way through the Research Facility with Pikachu in tow. Some time later, the two are ambushed again, this time by Ridley. After defeating her nemesis once again, Samus discovers two R.O.B.s transporting a Subspace Bomb from another area of the Isle of Ancients; presumably, she began investigating that area as well.

Later, Samus's storyline is revisited as she infiltrates the Subspace Bomb Factory along with Pikachu. After going through part of the Factory, they confront the Ancient Minister, who does not attack them. Shortly afterwards, Captain Falcon, Captain Olimar, Donkey Kong, and Diddy Kong all arrive, having entered the Factory via a different route. Samus is present when the Ancient Minister reveals himself to be R.O.B. in disguise, prompting an attack from Subspace forces under Ganondorf's command. After the battle, Samus and the rest must escape before the Subspace Bombs explode, so they make their way to Captain Falcon's Falcon Flyer. While flying out of the Isle of Ancients, however, the group is ambushed by Meta Ridley and must defeat him in 2 minutes.

When the Subspace Gunship appears, Samus's Gunship is one of the vehicles seen entering the portal to Subspace. Samus is one of many characters that travel through Subspace to confront the Master Hand. She is present when Tabuu reveals that he has been the one pulling the strings—literally—during the entire Subspace Emissary. Samus, along with everyone else, is subsequently turned into a trophy by Tabuu's Off Waves and is revived by Luigi, Ness, and King Dedede. Finally, Samus is one of the characters to make it through the Great Maze and confront Tabuu at the end. She is last seen standing on a promontory with the rest of the characters looking at what remains of the Isle of Ancients; the amount of Subspace Bombs that went off inside it has rendered it unable to be restored.

Bosses

 * Petey Piranha - Originates from the Mario franchise.
 * Rayquaza - Originates from the Pokémon franchise.
 * Porky Minch - Originates from the EarthBound franchise.
 * Galleom - A character original to Super Smash Bros. Brawl
 * Ridley - Originates from the Metroid franchise.
 * Duon - character original to Super Smash Bros. Brawl
 * Meta Ridley - Originates from the Metroid franchise.
 * Tabuu - A character original to Super Smash Bros. Brawl. Tabuu is the main antagonist and the final boss of The Subspace Emissary.

Ridley became a playable character in Super Smash Bros. Ultimate, with Meta Ridley as two of his alternate costumes. Galleom returns as a boss in Classic Mode and World of Light, while Petey Piranha is a part of Piranha Plant's Final Smash.

Cutscenes with Samus
In a dimly lit room, Zero Suit Samus kicks an air vent grate in the ceiling down, and emerges from the vent. She examines her surroundings, and her name flashes across the screen (as it does for every character upon their introduction). Arming her Paralyzer, she runs off into the facility.
 * Zero Suit Samus Infiltrates

Zero Suit Samus rushes into a room, searching for hostiles. The door locks behind her. She suddenly hears an electrical surge, and sees a power generator with a Pikachu trapped inside. Seeing that the creature is in extreme pain as the machine harnesses its electrical energy, she smashes the machine with her Plasma Whip and frees it. This triggers an alarm, prompting an army of R.O.B.s to intervene. Zero Suit Samus and Pikachu prepare to fight.
 * The Pikachu Generator

Entering a control room, Zero Suit Samus and Pikachu discover that Samus's Power Suit is in a research tube smewhere in the facility.
 * Where is the Power Suit?

Reaching the Power Suit, Zero Suit Samus and Pikachu approach it. The bridge they crossed retracts, trapping them on the platform. Two purple duplicates of Samus's Power Suit ambush them. The real Samus and Pikachu ready to fight them. Sector 1 begins to play as the two Samus copies appear.
 * The Copied Power Suit

Following the battle, an alarm blares. An army of R.O.B.s charge at Zero Suit Samus and Pikachu, but she wipes them out with an explosion and emerges from the room in her Power Suit, as Samus. She looks at Pikachu beside her, and her eyes can be seen through her visor momentarily as the two leave. Theme of Samus Aran, Space Warrior begins playing as Samus observes her suit before wearing it.
 * Samus Revived

Emerging in a room with a tall cylindrical shaft, Samus is suddenly ambushed by Ridley. He brings her into the air and drags her forcibly across the wall, damaging her Power Suit. Pikachu uses Thunder on Ridley, electrocuting him and causing him to release Samus. After falling to the floor, the three of them prepare to battle. It should be noted that the way Samus lands on the floor resembles her animation in her weakened state during the final boss battles of Super Metroid and Metroid Fusion.
 * The Destiny of Ridley and Samus

After defeating Ridley, Samus and Pikachu emerge from the Research Facility into daylight. They examine the environment, before noticing two R.O.B.s bringing a Subspace Bomb out of a small tunnel. They proceed to enter it. Samus and Pikachu race through the facility as an alarm blares. Samus runs in this cutscene much faster than she does ingame, but does not appear to be using her Speed Booster.
 * Ruins on the Island of the Ancients
 * In the Subspace Bomb Factory

Samus destroys a wall and emerges with Pikachu into a factory room. They confront the Ancient Minister and his army of R.O.B.s. The Minister looks saddened, puzzling Pikachu and Samus.
 * The Melancholy of the Ancient Minister

Donkey Kong, Diddy Kong, Captain Falcon and Olimar intervene, helping Samus and Pikachu. Ganondorf, through a hologram, orders the R.O.B. army to arm the Subspace Bombs. The Ancient Minister attempts to stop them, but the R.O.B.s are commanded to ignore him, and when this fails, fire upon him. The saddened Minister catches fire as the bombs are armed. Samus attempts to pull a R.O.B. off its bomb with her Grapple Beam, to no avail. After the Minister reveals himself to be a R.O.B., he joins Samus and the other fighters to repel an attack by the Subspace Army.
 * Ganondorf Takes Command

The fighters are unable to disarm the bombs. Captain Falcon arms his ship, the Falcon Flyer, and gestures for Samus and the other fighters to follow him, which they do.
 * The Countdown Will Not Stop

The fighters descend a long shaft and land in the Falcon Flyer, which quickly takes off. They are followed by Meta Ridley, who roars at the camera before the cutscene ends.
 * The Falcon Flyer

Samus's Gunship follows the Falcon Flyer, Fox and Falco's Arwings, Halberd and Hoctate Ship in an attack on the Subspace Army's massive battle ship. Their actions cause the battle ship to concentrate fire on them, allowing Kirby to gut the ship using a Dragoon. Ganondorf and Bowser, captains of the ship, retreat into the Subspace Portal behind them, followed by Samus's Gunship and the other ships.
 * The Great Invasion

Samus, and all the other fighters in the game (except for Toon Link, Jigglypuff and Wolf) ready themselves to explore Subspace.
 * At the Entrance to Subspace