Tournament:Mainstage 2021

Mainstage 2021 was a Super Smash Bros. Ultimate supermajor and Super Smash Bros. Melee major held in Ontario, California, from November 12th-14th, 2021. It was Beyond the Summit's second Smash tournament outside of the Smash Summit tournament series. The top 6 non-invited players for Melee and Ultimate qualified for and, respectively. The tournament also ran a  singles bracket. The tournament had the largest attendance of a SoCal Super Smash Bros. tournament, beating.

A Project+ event was planned, but was cancelled following Nintendo's takedown of 's Project+ event.

Super Smash Bros. Melee singles
(559 entrants) Top 64 Bracket 1 Top 64 Bracket 2 Top 16 Bracket

Super Smash Bros. Melee doubles
(102 teams) Top 32 Bracket Top 8 Bracket

Super Smash Bros. Ultimate singles
(830 entrants) Top 64 Bracket 1 Top 64 Bracket 2 Top 16 Bracket * DQ'd in losers.

Super Smash Bros. Ultimate doubles
(143 teams) Top 32 Bracket Top 8 Bracket

Trivia

 * was going to Mainstage 2021, but due to a car crash, he was unable to attend and was DQ'd.
 * This is the highest placing for a solo at a supermajor, with  placing 3rd.
 * This is also the highest placing for a solo at a supermajor, with  winning the tournament. It also marks the first time Leo has won a supermajor with a single character since  nearly two years prior.
 * The two players who were in Grand Finals (MkLeo and Sparg0) were the same ones in 2 weeks prior.