Assist Trophies

Assist Trophies function very similarly to Poké Balls. However, no Pokémon come out of them, and once an Assist Trophy is grabbed, it is automatically activated, 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 Gray Fox from Metal Gear. Unlike the Poké Ball, this item can be eaten by moves such as Kirby and King Dedede's Inhale, and Munchlax. In Smash 4 and Ultimate, all of the Assist Trophies in the base game are available from the start.

The majority of Assist Trophies in Brawl were undamageable, with only Starfy and Lakitu being able to be interrupted or otherwise hit or even KO'd. In Super Smash Bros. 4, however, some Assist Trophies could be attacked, potentially interrupting their attacks or otherwise manipulating how they perform and even being able to KO them (this can be seen by their ending animations coming earlier than normal, them having their own death animation, or simply teleporting away). However, there is no reward for KOing an Assist Trophy. In Super Smash Bros. Ultimate, more than one Assist Trophy can be on the stage at once. A larger number of Assist Trophies were also made able to be KO'd, which grants the player who KO'd them one point. When the Assist Trophy is close to becoming KO'd, the player who summoned it can KO it to prevent other players from gaining a point. In addition, certain Assist Trophies now have the ability to teleport on command, such as teleporting closer to an opponent when too far away or when crossing a blast line.

Trivia

 * Despite containing living things in them, Wario can eat Assist Trophies with Chomp.
 * Little Mac, Dark Samus, and Isabelle are the only Assist Trophies in the series to become playable characters in later installments.
 * However, BrawlFan1 has given movesets to Alucard, Bomberman, Isaac (Golden Sun), Knuckles, Shadow, Shovel Knight, and Waluigi, all of which are currently Assist Trophies in Ultimate.
 * Isaac (Golden Sun) and Gray Fox are the only Assist Trophies to skip an installment in the franchise and return in a later game. Interestingly, both were referred to as "newcomer" Assist Trophies on the Ultimate website.
 * Andross, Devil, Dr. Wright, Hammer Bro, Jeff, Knuckle Joe, Lyn, Metroid, Nintendog, Samurai Goroh, and Starfy are the only Assist Trophies to appear in all three games since their introduction in Brawl.
 * Likewise, Infantry and Tanks, Kat & Ana, Lakitu and Spinies, Saki Amamiya, and Tingle are the only Assist Trophies that have appeared in two installments, but are absent in Ultimate.
 * Magnus and Elec Man are the only Assist Trophies that appeared only in Super Smash Bros. 4 and did not return in Ultimate, excluding the assists-turned-playable Isabelle and Dark Samus.
 * The Yoshi and Pokémon series are the only "Original 10" universes to have no Assist Trophies.
 * However, the Pokémon series uses Poké Balls, making the Yoshi series the only one in the "Original 10" to have no item-based assist characters whatsoever.
 * Final Fantasy is the only non-DLC third-party universe in Ultimate with a playable character to not have an Assist Trophy.
 * The other universes that do not have any Assist Trophies are Ice Climbers, Game & Watch, R.O.B., Wii Fit, Mii, Duck Hunt, and the DLC universes in Ultimate, except for ARMS.
 * However, BrawlFan1 has made a concept for Creeper from Minecraft, which is a DLC universe, as an Assist Trophy.
 * Hammer Bro is the only Assist Trophy character to appear as an enemy in the Subspace Emissary.
 * It is also one of five Assist Trophies to appear as an enemy in Smash Run, along with Starman, Lakitu and Spinies (albeit using their 3D designs), Chain Chomp, and Metroid.
 * The Mega Man franchise has the most Assist Trophies out of any third-party franchise at 3, with Elec Man appearing in Smash 4 and Zero and Wily Capsule appearing in Ultimate.
 * The Animal Crossing franchise is the only franchise to have a different Assist Trophy in each game, with Mr. Resetti appearing in Brawl, Isabelle appearing in Smash 4, and Kapp'n appearing in Ultimate.
 * In Brawl's Classic Mode, if the character who summoned an Assist Trophy is KO'd, the Assist Trophy disappears. However, this does not happen in All-Star Mode.
 * In the Smash Direct for SSB4, Waluigi was shown as a Wario series Assist Trophy, despite never appearing in a Wario game. By the game's release, he was corrected to represent the Mario series, like in Brawl.
 * In SSB4, the silhouette figure within the Assist Trophy capsule will occasionally blink its eyes.
 * In the GameCube preview issue of Electronic Gaming Monthly, the Super 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 [1].
 * Prior to the Ultimate 2.0.0 Update, if two Isabelles used Fishing Rod to grab onto an Assist Trophy, one would grab on, and the other would not; however, the result would be the former infinitely spawning the same Assist Trophy until she got hit.
 * Not counting Rathalos, who is fought as a boss, Rodin, Samurai Goroh, Phosphora, and Spring Man are the only Assist Trophy characters to not appear in any Spirit battle.
 * Out of all of these, Spring Man is the only one whose Spirit has a spirit battle, as Rodin, Samurai Goroh, and Phosphora are all summon-exclusive.
 * In Ultimate, many Assist Trophies cannot appear on certain stages, either due to complications with the stage or the character already appearing in the background of the stage. Training, Battlefield, Small Battlefield, Big Battlefield, Mushroom Kingdom, Yoshi's Island, Skyworld, Windy Hill Zone, Yggdrasil's Altar and Northern Cave are the only stages where every Assist Trophy can appear, mainly due to the fact that there are no stage hazards, obstacles and/or features on those stages that hinder the Assist Trophies.
 * Additionally, Battlefield versions of certain stages will feature every Assist Trophy.