*raises hand* I don't know anything about American sports on account of not being American.
You know for all his apparent popularity I've seen very little talk about Isaac in this thread. I've never played Golden sun so I don't really know what he'd be like other than having a sword and using a giant hand blast. (shove?) So what exactly would he be likely to be like in smash?
In the Golden Sun games, there are rare people, known as adepts, who have the power of psynergy. Psynergy allows for control over the elements as well as various other powers, depending on the adept's elemental alignment.
Isaac has telekinetic powers, as seen from his assist trophy in Brawl. His telekinesis is often represented as a giant white glove, which he can use to push, pull, grab, lift, carry, and pound objects. His other major focus is his control over earth. He can fight with everything from earthquakes to boulders to thorny vines. Technically, he can use the other elements as well depending on his current class, but he's primarily an earth adept.
The first minute of this video shows of some of what Isaac can do (although that is techinically Isaac's son, Matthew, in the video). This is from the DS game, Dark Dawn.
These two videos show off all of the battle psynergy from the first two GBA games.
Even some of the weapons have flashy abilities in the Golden Sun games. This is a compilation of all of the special weapons in the GBA games. Worth noting are 0:43 (Gaia Blade) and 4:17 (Sol Blade), as these are the best earth-aligned weapons in the first and second games respectively, so Isaac might end up wielding one of those as his weapon.
Adepts can also summon gods and demons (and colossal nuke-launching robots) in the fight. Worth noting is Judgment (4:23) is the strongest earth-only summon.