Isaac (ロビン, Robin) is the main protagonist of Golden Sun for the Game Boy Advance. His appearance as an unlockable Assist Trophy in Super Smash Bros. Brawl is his (as well as any Golden Sun character's) first appearance in 3D, the first time his voice was heard (being, again, the first appearance of any Golden Sun character's voice as well) and was the only appearance of Golden Sun in any official format between 2002 and 2010.
Isaac originally appeared in Golden Sun, an RPG-style game for the GBA. The game focused on Isaac and friends' quest to retrieve the four elemental stars and stop the return of Alchemy, following their theft by the games' first two antagonists, Saturos and Menardi. Isaac is the main playable character in the game, and he is one of the four playable characters capable of wielding Psynergy, a form of mind power. Isaac is a Venus Adept, meaning he can manipulate Earth and plants. As the game progresses, Isaac and friends gain access to a wider variety of Psynergy necessary to progress through the game.
Isaac returns in the game's sequel, Golden Sun: The Lost Age, but instead appears as one of eight party members led by the game's protagonist, Felix. This game explains the story from Felix's point of view, and focuses on Felix and the full party as they are forced to return the flow of Alchemy to save their parents' lives, which are being threatened by the game's new antagonists, Karst and Agatio, as they continue what Saturos and Menardi could not after their death in the first game.
He also briefly appears in the most recent game in the series, Golden Sun: Dark Dawn, this time as the father of the main character, Matthew. While he joins Matthew's party at the beginning of the game, he is not seen for the rest of the game's plot.
The Psynergy that Isaac uses in Brawl is called Move. It is a Utility Psynergy - that is, it cannot be used in battle, and it is acquired virtually at the start of the game. "Move" is used primarily to move heavy objects to solve puzzles. The use in Brawl is somewhat different; while it does move obstacles, it simply pushes them away in order to achieve a wide variety of different ends.
In Ultimate, the additional Psynergy that Isaac can use are called Teleport and Pound. Both originated from the sequel game, Golden Sun: The Lost Age. Unlike Move, which is an innate ability, Pound can be learned by equipping the Pound Cube, and Teleport can be learned with Teleport Lapis. Also, like Move, both Pound and Teleport's usage in the original game versus in Ultimate are different, as in The Lost Age, Pound's primary use is to solve puzzles by flattening wooden posts and destroying stone pillars, and aside from impeding certain Djinn from advancing to an inaccessible area, it lacks offensive means, while Teleport is generally used to access secret areas via stone circles, with the ability to revisit past towns as a secondary bonus.
In Super Smash Bros. Brawl
As an Assist Trophy
When Isaac appears, he uses a Psynergy spell called "Move" as his in-game battle effect, which creates an energy field that pushes foes away and off the stage. If the player is hit by Move, it can be difficult to escape. Isaac will turn to face enemies during this attack should they attempt to evade. However, like in the Golden Sun series, the move does no damage. Isaac performs Move three times before vanishing.
Unlike many other Assist Trophies, Isaac can affect invincible opponents, since his Psynergy pushes the opponent and does no damage. If the Psynergy makes contact with a Smash Ball, the sound of the Smash Ball being hit will play, along with its visual effects.
To unlock Isaac, players must play 200 matches to completion.
A strong-willed Psynergy adept of the bloodline of an ancient race thought to have been lost with the downfall of civilization. He can manipulate earth-based forces and is also a highly skilled swordsman. He sets out to protect a lighthouse that can release the sealed powers of alchemy. In Smash Bros., he uses "Move" Psynergy, which creates an energy field that pushes foes away.
As an Assist Trophy
After being absent from Super Smash Bros. for 3DS/Wii U, Isaac returns to Ultimate with a slight redesign to his appearance, mirroring his original Golden Sun artwork. In addition to using the Move Psynergy from Brawl, he also is capable of using Pound, another Utility Psynergy, as well as a unique ability similar to the Lift Psynergy where he grabs an opponent and takes them off the stage. The usage of Pound means that Isaac is now capable of causing damage to opponents, which deals an average of 12.0% damage to fighters.
Isaac's mechanics in Ultimate versus Brawl are more advanced. As opposed to remaining stationary and using Move three times, Isaac now uses Teleport to move around the stage and can perform one of three different Utility Psynergies; Move, Pound, and a variation on Lift. Move appears to remain his most used of Psynergies, as it retains the pushback it had in Brawl. Lift operates similar to the Beetle where it can lift a fighter above the top boundary line and also has an animation of the hands failing to capture the fighter, as well as when the fighter breaks free from the grip.
Isaac, like some Assist Trophies in Ultimate, can now be KO'd and also can be covered in ink by any of the Inklings' special moves or the Killer Wail Final Smash. However, in spite of his ability to use Teleport, he can manually return to the stage when knocked back, as well as perform evasive maneuvers such as air dodges.
As a costume
Isaac is also the basis for a costume for Mii Swordfighters.