Following Microsoft’s acquisition of Bethesda on September 21, 2020, Vault Boy is now retroactively the first Microsoft Mii Costume, and Fallout the second Microsoft franchise to be represented in Smash.Vault Boy is the first time Bethesda has been represented in Super Smash Bros.

This is a reference to Dogmeat, a recurring dog companion throughout the Fallout series. Finally, Vault Boy stands besides Duck Hunt. Later, Vault Boy fights Dark Samus, referencing various mutant enemies seen in the Fallout series he is later been KO'd by a grenade, a running gag of how in every S.P.E.C.I.A.L trailer, Vault Boy was killed in the end. This is a reference to a thumbs-up being Vault Boy's signature pose.

In his reveal trailer, the opening features Mario performing his thumbs-up taunt. Unlike Sans and Cuphead, Vault Boy does not come with a music track, possibly due to most of the music in the Fallout series being licensed music. His Vault Suit is labeled '111' on the back, a reference to the Sole Survivor's vault in Fallout 4. His gun appears to be based off the generic gun he is depicted with on the Energy Weapons bobblehead, a collectible item in the Fallout games. His 'mask' is just his head instead of a mask with the Mii's head visible.

Like Sans and Cuphead before him, Vault Boy appears as a fully modelled character. A DLC costume for Mii Gunner based on the Vault Boy was announced on June 22nd, 2020, and was made available for purchase on June 29th, 2020.

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