Assist Trophy is an item that, when grabbed, summons an Assistant Character that does an effect to help the summoner before disappearing. The effect can be anything from direct attacks to indirect techniques, usefulness ranging from deadly to near useless.
The Last Airbender
Summons a slow, harmless rock.
Big Rigs: Over the Road Racing
Drives (literally) around the stage.
Chester A. Bum
That Guy with the Glasses
The Adventures of Sonic the Hedgehog
Throws footballs everywhere.
Tom and Jerry
Slowly creeps toward an opponent, and deals an unseen attack while the lights dim.
Nayarit en Línea
Repeatedly yells "FUAAAA!". Can push opponents away and revive teammates in stamina battles.
Zaps lightning from the sky.
Punches and summons orbs to attack. Teleports toward opponents as well.
El Chavo del Ocho
Childishly puts his hands up and punches forward / backwards thrice.
Angry Video Game Nerd
Swings his guitar forward after it gets zapped by lightning.
Super Mario Brothers Supa Show
Hops and fireballs.
Plays music from his van, which causes nearby opponents to dance and enter the van, which either drives off the stage or explodes against a wall.
Turns into Uboa after awhile, which insta-kills when touched.
Talks about his diabetus, which makes opponents sleep. He then throws away his ice cream and pies for opponents to eat.
Shoots electric beams at mirrors.
Uses a grappling hook to pull opponents toward herself.
The John Show
Makes someone's head explode when awoken, for some reason.
The Fairly Odd Parents
Tries to capture an opponent's powers with a net to use them in a magic suit of combat.
JoJo's Bizarre Adventure
Has a random chance to replace an Assist Trophy when they're touched, and proceeds to crush the touching opponent with a steamroller.
Brawl in the Family
Sweeps-away items and traps for a bit, then gets crushed by a thwomp.
Throws various kinds of eggs.
Shoots forward. Shots' effects have a chance of being delayed for a few seconds.
Captain N: The Game Master
Hits players with a bat, and can teleport.
Throws potions that change an opponent's stats to that of another opponent's. Doesn't like getting attacked.
Gets hit in the testicals with a football, causing opponents to laugh.
The Big Bang Theory
Launches an opponent (or his mother's meatloaf if nobody goes near) from his Space Toilet.
Throws a barrage of eggs.
I Like Trains Kid
Causes a train to run him over, along with anyone in the way.
Can shoot, dance, speech, or "HALLELUJAH!".
The Emporer's New Groove
Dances, and throws opponents off the stage if they mess up his groove.
Star vs. the Forces of Evil
Stays in-front of his summoner and combo-attacks any enemies who get close.
Summons his minions to go and kill.
Phineas and Ferb
Targets an opponent to aim his attacks at.
Flickers the stage's lights on-and-off for a while.
Fires a rainbow beam from his stomach.
Thin Cat & Fat Cat
Fat Cat leaps towards Thin Cat, damaging anyone in the way.
Will It Blend
Determines if an opponent will blend in his blender.
Toon Funky Kong
Donkey Kong Country Cartoon
Flies around on his plane to drop barrels that explode when attacked.
Moves around frantically to attack opponents with either a baseball bat or bricks, making them drop collectable coins.
Tries to throw his summoner back-onto the stage if they fall down.
Lawl Liquid Crystal