Biggs is a Mii from the Switch.
Biggs appears as one of the Miis that are fought in the Sephiroth DLC Spirit Board in Super Smash Bros. Ultimate since update 10.1.0, and he hasn't appeared in any game since. His Mii data file filename is edge_spirits_mii09.bin, with "edge" standing for Sephiroth.
His Mii name in his Mii data file is ビッグス.
His Mii ID is as follows: ED 67 CB 23 FF 3E 43 4C A0 D5 BD 07 6B E5 C9 C3
His Mii data file contains unused Mii data. In-game, his Smash color is set to black (as Smash Ultimate can save a favorite color separate from a Mii's actual favorite color), but his Mii data file has his favorite color set to red.
Biggs makes an appearance in one spirit battle, unlocked on the DLC Spirit Board if Fighters Pass 2 or Sephiroth's DLC is purchased. He will appear in the spirit battle for the spirit "Barret", alongside Jessie (Switch) (who is holding a Bob-omb) and Wedge, and after all three are defeated, Barret. The Barret Mii Fighter must be defeated for the player to win.
His Smash color is black, and in battle, he always appears as a Brawler and wears the Protective Gear with no headgear. His neutral special is set to 3 - Exploding Side Kick. His side special is set to 2 - Suplex. His up special is set to 1 - Soaring Axe Kick. His down special is set to 2 - Feint Jump. (Moveset: 3212.) You can see a screenshot of how he appears in-game on the left.
Biggs unfortunately does not appear as a Mii in any promo art released. However, he does appear as his human character in promo art for Final Fantasy VII Remake, which can be seen on the left.