An Assist Trophy is an item that, when grabbed, summons a Nintendo character out of twenty seven choices of various origin to quickly aid the holder, though there are currently three third party Assist Trophies, not to mention some assistants get in the way more than they help. Assist Trophies work nearly identical to Poké Balls. However, no Pokémon come out of them, and once an Assist Trophy is grabbed, it is automatically activated (though this is not very convenient), assuming the holder is standing on the ground, and not in a jump, attack, or hitstun. Some assist trophies must be unlocked in order to be used, such as Isaac from Golden Sun. Unlike the Poké Ball, this can be eaten.
Only one Assist Trophy (and the character it releases) can be in a match at once. The next Assist Trophy will not appear until the data for the character it will release is fully loaded.
Andross - Andross appears in the background and shoots tiles at the players.
Barbara - Barbara strums on her guitar creating damaging soundwaves, similar to Konga Beat, but with less range and duration. Unlock: Obtain twenty five Songs
Devil ("Demon" in Europe) - Devil moves the stage boundaries. However, Hoop Damage is not added if you are out of the boundaries the Devil creates.
Dr. Wright - Doctor Wright summons buildings to rise up out of the ground. This damages opponents who are standing in the area of the building, and produces great vertical knockback. Occasionally makes a massive skyscraper.
Excitebikes - Excitebike racers ride around the stage causing damage to those they collide with. Some of them, if on a stage with an edge, will go back and forth until their time runs out.
Gray Fox ("Cyborg Ninja" in Japan)- Frank Jaeger, the Gray Fox, runs around slashing opponents. Also reflects stray projectiles. Unlock: Unlocked with Snake
Hammer Bro - Hammer Brother throws hammers at opponents.
Helirin - Helirin floats around the stage while rotating, acting as a wall.
Infantry & Tanks - The Advance Wars infantrymen and tank sprites roam across the stage shooting at players. When spawning, they follow the direction of the summoner. Unlock: Play 300 Brawls
Isaac ("Robin" in Japan) - Isaac pushes opponents off the stage by using a skill called Move, represented by giant magic hands. It can be dodged and escaped. However, escaping is just about impossible unless you're on the tip of the hand. Unlock: Play 200 Brawls
Jeff - Jeff Andonuts shoots 5 homing rockets from his Multi Bottle Rocket five invention (four small and one large) at his opponents.
Jill ("Dori Kururi & Rasanda 8" in Japan) - Jill attacks opponents with her drill.
Kat & Ana - Kat and Ana fly in different directions slashing at anybody in front of them, but always cross in the same spot.
Knuckle Joe - Knuckle Joe delivers a series of Vulcan Jabs to his opponents and finishes with either a Smash Punch or an uppercut attack named Rising Break.
Lakitu and Spinies ("Jugem" in Japan) - Lakitu drops Spinies onto the field. Upon landing, the Spinies walk around giving damage to opponents. Lakitu can be knocked off the screen or killed.
Little Mac - Little Mac runs around punching opponents.
Lyn - The screen darkens, as Lyn focuses and then having teleported, she delivers a single, powerful strike focused on the nearest opponent, similar to Galaxia Darkness in animation and knockback.
Metroid - A Metroid latches onto players and gives them damage. Can be attacked and shaken off, but prevents the victim from using recovery moves. However if done right, the character can spam recovery moves indefinitely until the Metroid disappears.
Mr. Resetti - Mr. Resetti gives speeches about different topics. If attacked, he will keep talking. If attacked too much, he causes an explosion.
Nintendog - A "Nintendog" (Labrador Retriever) blocks the screen.
Ray MK III - Ray MK III flies around the stage shooting missiles and green energy bullets. Unlock: Play 100 Brawls
Samurai Goroh - Samurai Goroh slashes his swords while chasing opponents.
Saki - Saki Amamiya slashes and fires with his Dolphin Gun.
Shadow the Hedgehog - Shadow slows down time with Chaos Control, similar to the Timeritem, but with shorter duration. The summoner continues to move at normal speed. Unlock: Unlocked with Sonic
Starfy (known by its JP name, Stafy in the game) - Starfy spins, hurting players. Can be knocked off stage.
Tingle - Tingle randomly summons a variety of strange effects (see article)
Waluigi - Waluigi repeatedly stomps players into the ground. This onslaught is followed by either a strong kick or a strike from his tennis racket.
In addition to the above characters, scrapped Assist Trophy data for Ridley was found when hacking Super Smash Bros. Brawl. Attendants at the 2007 Whobby Game Festival claimed to have seen Assist Trophies of Duster, Muddy Mole, and Rosalina, but this was proven to be fabricated upon the release of the game.
A capsule that contains characters who will help you out in battle. You won't know who's in the capsule until you open it. It may be someone everyone knows or someone who's a bit of a mystery. The majority of these characters are invulnerable, so attacking them is not an option. You know what that means, right? RUN!
In Classic Mode, if the character who summoned an assist trophy dies, the assist trophy goes away. However, this does not happen in All-Star mode.
In the Gamecube preview issue of Electronic Gaming Monthly, the Smash Bros Melee article comments that Nintendo originally tried to implement Assist Trophies in Melee. The only trophy concept they gave details on was one that would release the ducks from Duck Hunt to fly around the stage and interfere with the fighters.