Assist Trophies
Assist trophies are basically Pokéball clones that appear on the field in a brawl. If you throw them, a random assist character will pop out and help you. Well, most will help you, anyway. Think of them as the Smash Bros. version of summon creatures. These are the ones we know about thus far (in no particular order):
Hammer Bros.
Super Mario Bros.
Anyone who's ever played the original Super Mario Bros. on the NES (or one of its ports) should be able to remember these guys... And shudder! They often appeared in pairs and would mercilessly pelt you with a barrage of hammers like a wall of raw, undiluted pain.
They appear to function pretty much the same in Brawl, tossing their hammers at enemies. Some E for All demo players have reported that can appear alone, or in pairs.
They were featured in the Dojo entry that introduced assist trophies.
Nintendog
Nintendogs
A yellow labradore retriever from Nintendo's 6+ million seller hit, Nintendogs. This little guy appeared as the first assist trophy in the original E3 trailer, although Brawl fans didn't yet know what an assist trophy was yet.
He doesn't seem to do much but get in the way...
The Nintendog was also featured in the Dojo entry that introduced assist trophies.
Samurai Goroh
F-Zero
Captain Falcon's rival and fellow F-Zero pilot. In the F-Zero series, he drives the #05 Fire Stingray. He had the honor of being the first major assist trophy to be unveiled, introducing Brawl fans to the exciting new gameplay element (and crushing their hopes of him being a playable character).
In Brawl, Goroh attacks enemies using his sword.
Dr. Wright
Sim City
Named after the legendary game designer Will Wright, Dr. Wright appeared as your assistant in the SNES port of Sim City.
When summoned, he'll conjure a group of skyscrapers out of the ground, causing fighters to shoot into the sky.
Knuckle Joe
Kirby
Knuckle Joe is often just a simple enemy in many of the Kirby games, however he has taken on the job of an assistant in a handful of Kirby titles, most notably, Kirby Super Star.
When summoned, he appears to have a small number of moves that he can perform randomly.
Devil
Devil World
Even Satan himself shows up in Super Smash Brawl. Talk about freaky... Wait, is he even a Nintendo character? Actually, he's from the Japanese-only NES game Devil World, where he danced on the top of the game screen as the antagonist for "Tamagon", a dragon controlled by the player.
In Brawl, he causes the screen to scroll, forcing fighters to keep up. To quote Sakurai, "Here’s an Assist Trophy that throws common sense out the window. I mean, he’s not assisting at all!" He does not seem to affect the stage's boundries, so you won't get KO'ed by moving off the screen.
Andross
Starfox
Andross functions as the villian in the first two Starfox games for the SNES and N64, as well as an appearance in Starfox Adventures. The form he takes in Brawl is based directly on the final battle in Starfox for the SNES.
When summoned, he will move into the background and begin spitting polygons towards the playing field.
Lyn
Fire Emblem
Many were the poor, unfortunate souls to learn that this swordmaster would not be a playable character in the next Smash Bros. game. Lyn was one of the three main characters in Fire Emblem for the GBA, the seventh game in the series, but the first to reach western shores thanks to the popularity of none other than Marth and Roy. The irony, of course, is that Marth was not in the game at all, and Roy only made a brief cameo as a child at the end of the game.
When first summoned, she won't attack right away, instead opting to stand by and wait. Then, without warning, she strikes down the enemy!
Mr. Resetti
Animal Crossing
This eerie little mole would show up in Animal Crossing if you ever reset the game or turned off the power without saving. Talk about creepy, he'd even go so far as to fake wiping your save card!
His exact role in Brawl is unknown, but he will talk a lot when summoned...
Excitebike
Excitebike
Motocross racers from the 1985 NES classic Excitebike. "It's a new record!" You'd think they could have at least give them a quick 3D model, but instead they opted to just rip their sprites from the original game...
Here in Brawl, they'll drive along in hordes and try to push you off the stage.
Lakitu
Super Mario Bros.
These guys are to the Super Mario series what Like-Likes are to Zelda. Well, sort of. In most of the Mario games, Lakitus appear in the sky and rain spiked balls down on the player that spawn into "spinies" when they hit the ground. Spinies a little red, spiked turtle things that are nothing short of a headache for Mario. They reprise this role for Brawl.
Lakitu was revealed in the Excitebike entry on the Smash Bros. Dojo.
Little Mac
Punch-Out!!
Trained by "Doc Louis", Little Mac is a spirited fighter who challenges a lineup of fictional boxing champions (with the exception of none other than Mike Tyson as the final match in the original NES version). He also appeared in the less-remembered Super Punch-Out!! for the SNES with blonde hair and made a cameo appearance in EA's Fight Night: Round 2 for the Nintendo Gamecube. His look on Brawl is based directly on the NES version.
In Brawl, Little Mac will charge and pummel enemies using his boxing moves from the games.
Advance Wars Units
Advance Wars
These little grunts are from the Advance Wars series of games where they fought tirelessly to win the battle under you command. They're ripped directly from the map sprites in the GBA games.
They drop from the sky and shoot at enemies as they march forward. Thus far, they've only appeared in the E for All demo and have yet to appear on the Dojo.
Saki Amamiya
Sin and Punishment
With the planet in chaos, Saki fights his way through the N64 shooter title Sin and Punishment: Successor of the Earth. The game was recently released as an import title on the Wii virtual console.
A surprise for many, Saki was reported to be an assist trophy by media outlets and E for All attendees (although some say that it is Achi, not Saki). When summoned, he will run around the stage shooting, chasing down enemies.
Jill
Drill Dozer
Star of the critically acclaimed (but poor selling) GBA game, Jill is the daughter of the leader of a bandit gang known as "The Red Dozers", she's on a quest to retrieve the Red Diamond. She controls a giant drill bit that can be upgraded throughout her adventure.
In Brawl, Jill moves around the main platform and is able to jump at enemies, pushing them to the side and building up damage. She has not yet appeared on the Dojo.
Metroid
Metroid
The jellyfish-like titular creature of the Metroid series, and every bounty hunter's worst nightmare. Their spine-tingling squeal gives veteran Metroid players chills. Natives of the planet SR388, they latch onto their prey and drain their life force. In order to defeat them in most of the games, Samus must freeze them with her ice beam, then pound them with a barrage of missiles.
The Metroid reprises its role in Brawl, floating about the stage in a set pattern, latching onto anyone it comes across. It is difficult to get off once it's caught the player. The Metroid has not been given a Dojo entry yet.
Gray Fox
Metal Gear
Frank Jaeger, a FOXHOUND agent, sometimes friend and sometimes enemy of Solid Snake. Here, he dons his cyborg ninja exoskeleton that first appeared in Metal Gear Solid. (His name is spelled "Grey Fox" in some of the games, but the Dojo uses "Gray Fox".)
When summoned to the field of battle, he attacks like—you guessed it—a cyborg ninja! He also has the ability to reflect projectile attacks.
Stafy
The Legendary Stafy
Stafy the Starfish is the hero of the Japanese-only "Denetsu no Stafy" series, although he is often recognizable to North Americans due to his assorted cameos in other Nintendo games. The Stafy series is made up of several platformer games where the goal is often to retrieve items for various characters.
Not much is revealed on the Dojo about his abilities besides the fact that he has a fire attack, and can attacked by the playable characters.
Waluigi
Super Mario Bros.
If Wario is freaky (and he is), then Waluigi is in a class by himself. Created as an additional playable character for Mario spinoff titles, he frequently appears in Mario Golf, Mario Tennis, Mario Party, and Mario Kart titles. Watching him walk with those spider-like legs on the screen can put you into a trance from which you will never return...
He carries a tennis racket into battle here in Brawl, and pounds the player into the ground with his feet, kicking them aside afterwards.