As far as characters go, I just want Isaac from Golden Sun.
Both Golden Sun 1 and 2 sold over a million copies WW on the GBA (an achievement that took Fire Emblem and Xenoblade several installments and higher budgets to reach). You can see the evidence for that on this old Gaf thread here:
https://www.neogaf.com/threads/nint...dware-sales-data-from-1983-to-present.963700/
To add to that, Smash doesn't really have any original playable reps from the GBA generation (that I grew up from). For the west, GBA introduced Golden Sun, Advance Wars, and Fire Emblem to us for the first time (and Wario Ware, but I don't see Wario himself as a GBA offspring). GBA, in some ways, was like a portable SNES, having lots of remakes and ports of SNES games like A Link to the Past, Super Mario Bros. 2, 3, and World (based off All Stars), the old school Final Fantasy's, etc, and most of these games are still great today, so the GBA kids also loved Mario and company, but they don't really reflect the history of the Game Boy Advance generation.
Looking at Pokemon from that perspective, they got the Game Boy/Color era covered with Pikachu+, DS era with Lucario, and 3DS with Greninja. Rumor is the Switch Pokemon game will be a remake of Yellow, so... again, it's the Game Boy Advance that's got no show here.
Oh yeah, but there is Roy, from Fire Emblem 6, a game that the West never got. I remember anticipating that one badly after finishing and seeing the prologue in 7 (AKA just Fire Emblem in the west). The Roy game never came though.
Anyway, Golden Sun spoke to me the loudest of the GBA originals, and I and most others see Isaac as the face of that series, being the protagonist of the original. Pop culture wise, a popular cartoon series called 'Avatar: The Last Airbender' aired two years after Golden Sun: The Lost Age had released and carried a lot of that spirit Golden Sun had of special people carrying the ability to command elements to their whim.
Since Sakurai once said (
http://sourcegaming.info/2015/07/09/megaman-villager-wiifit/ ) that he has to be able to powerfully envision a character "dancing" in his head to able to realize them, I once proposed on Smash Boards that Toph from Avatar: The Last Airbender would be a good base to excite the imagination from:
Based on Camelot Software Planning's official Golden Sun artworks, this video is roughly how Isaac (who is an earth adept) would fight when not confined by the GBA's hardware limitations plus a turn-based combat system. Pikachu is a good reference of a character who had an anime to help further define his character outside his original Game Boy game.