Assist Trophy

Spawns a character to help you. The Assist Trophy (, Assist Figure) is an item introduced in Super Smash Bros. Brawl that, when picked up, breaks open and summons a random character to aid the user.

Overview
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. In Brawl, 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 Super Smash Bros. 4 and Super Smash Bros. Ultimate, all of the Assist Trophies in the base game are available from the start.

Assist Trophies fall into three basic categories. The most common type are characters that attack opponents directly. Once an opponent is targeted, the character chases them down and attacks them with a limited moveset. While these characters are often very powerful and capable of overwhelming the oppoenent, they are also very predictable, meaning they can easily be avoided and tricked. A majority of damageable characters are this type of Assist Trophy. The second type are characters that act on a set script and do not directly engage in the battle. They indirectly cause collateral damage from their actions, such as flying objects or explosions. The third type are characters that act in a support role to the summoner. They either grant status effects to the summoner or the opponent or both, or effect the appearance of the game itself. This is the rarest type of Assist Trophy.

The majority of Assist Trophies in Brawl are undamageable, with only Starfy and Lakitu being able to be interrupted or otherwise hit or even KO'd. In Smash 4, however, some Assist Trophies can 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 Ultimate, the number of damageable Assist Trophies was expanded to include nearly all that attack fighters directly. They now emit a yellowish aura when they are low on health, and grant the player who KO'd them one point as if they took an opponent's stock. When the Assist Trophy is close to becoming KO'd, the summoner can KO it to prevent other players from gaining a point. More than one Assist Trophy can now be on the stage at once, which introduced the concept of Assist Trophies fighting each other, as they are programmed as CPU characters and go after CPU characters as well. 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.

Either due to complications with the stage or the character's appearance in the background (e.g. because he's a vampire, which does not have a reflection, Alucard cannot appear in Wii Fit Studio, which features a giant mirror in the background, and because darkness would completely block out the drawings, Nikki cannot be summoned on stages that have a dark scenery (e.g. Gamer)), many Assist Trophies cannot appear on certain stages In Ultimate. The only stages where all Assist Trophies can appear are, , Small Battlefield, , , , Skyworld, Smashville, Windy Hill Zone, Yggdrasil's Altar and Northern Cave.

In Super Smash Bros. Brawl
There are 27 Assist Trophies in Super Smash Bros Brawl, 6 of which are unlockable.

In addition to the above characters, scrapped Assist Trophy data for Ridley was found when hacking Super Smash Bros. Brawl. In the final game, he was a boss in The Subspace Emissary.

In Super Smash Bros. 4
Assist Trophies return in Super Smash Bros. 4. They now sport their modern design, with a shorter, more iridescent design and a softer "popping" sound upon use, instead of the glass-shattering sound effect it had in Brawl. Unlike in Brawl, where no Assist Trophies apart from Starfy and Lakitu could even be damaged, let alone defeated, several Assist Trophies, including several returning ones who could not be attacked in Brawl, can now be KO'd. There are 39 Assist Trophies in total, with 21 new ones and 18 returning from Brawl, while nine were cut (with one of them becoming a fighter instead). Both the 3DS and Wii U versions include exactly the same Assist Trophies, and unlike in Brawl, there are no unlockable Assist Trophies.

In Super Smash Bros. Ultimate
For the first time in the series, multiple Assist Trophies can appear at once. Up to two Assist Trophies may appear on screen at a time but no two Assist Trophy items can summon the same character. Some Assist Trophies cannot appear at the same time as others. Players get points in Time battles when KOing a defeatable Assist Trophy. Occasionally, opposing Assist Trophies may fight each other. Assist Trophies also respawn if they fall off the stage accidentally. The item itself reuses the rainbow dome from SSB4, though the rainbow effect is more subtle, and it no longer has a bluish tint. There are 59 total Assist Trophies, with 27 new ones, 30 returning from SSB4, and two returning from Brawl after being cut from SSB4. Nine Assist Trophies from SSB4 were also cut (with two of them becoming fighters instead).

For various reasons (such as gimmicks affecting the Assist Trophy's visibility or abilities, already appearing as a background character, or even Alucard not appearing in front of mirrors), certain Assist Trophies are unable to spawn on certain stages.

Trivia

 * Little Mac, Dark Samus, and Isabelle are the only Assist Trophies in the series to become playable characters in later installments.
 * Isaac 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,, Nintendog, Samurai Goroh, Shadow, Starfy, and Waluigi are the only Assist Trophies to appear in all three games since their introduction in Brawl.
 * The and  series are the only "Original 10" universes that have never had any Assist Trophies.
 * However, the Pokémon series uses Poké Balls, making the Yoshi series the only one in the "Original 10" that has never had any item-based assist characters whatsoever.
 * The other universes that have never had any Assist Trophies are, , , , , , , and the DLC universes in Ultimate, except for.
 * The franchise has the most Assist Trophies out of any third-party franchise at 3, with Elec Man appearing in Smash 4 and  and Wily Capsule appearing in Ultimate.
 * 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 to fly around the stage and interfere with the fighters.
 * In the English version of the Super Smash Bros. Direct, Masahiro Sakurai was mistranslated as saying that Assist Trophies would "figure into All-Star Mode" in some fashion in Super Smash Bros. 4. However, Assist Trophies ended up playing no role in the mode, and they do not even spawn as regular items within battles. In Japanese, Sakurai was instead referring to the "all-star" cast as opposed to the mode itself.
 * Prior to the Ultimate 2.0.0 update, if two s 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 never to 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.