Multi-Man Smash

Multi-Man mode is a single-player mode in both Super Smash Flash (as Multi-Man Melee) and Super Smash Flash 2 (as Multi-Man Brawl) which challenges the player to defeat as many enemies as possible without falling off the stage, being knocked out, or self-destructed. The mode was first presented in Super Smash Bros. Melee and was later incorporated into Super Smash Bros. Brawl too.

List of Multi-Man modes

 * 10-Man mode: Challenges the player to defeat 10 opponents. It is the shortest of all the Multi-Man modes as it only takes seconds to beat all the opponents
 * 100-Man mode: Challenges the player to defeat 100 opponents. It usually takes a few minutes to beat all opponents.
 * 3-Minute mode: Challenges the player to defeat as many opponents as possible within 3 minutes.
 * 15-Minute mode: Challenges the player to defeat as many opponents as possible within 15 minutes. It one of the more difficult Multi-Man modes considering the long time can lead to a very weakened player, which facilitates being knocked out by incoming opponents.
 * Cruel mode: Challenges the player to defeat as many opponents, with high handicaps on the player and increased aggressiveness and knockback ressitance on the opponents, before being knocked-out or self-destruct. It is the most challening of all the Multi-Man modes.
 * Burly-Brawl mode: Exclusive to Super Smash Flash. Challenges the player to defeat as many opponents as possible before being knocked out or self desctruct. It has no time limit. Unlike Endless mode (which it replaced), only a single type of fighter is fought.

In Super Smash Flash
The opponents faced in Super Smash Flash are grey-shaded versions of the playable roster, colloquially called the "Fighting Shadow Team" as they go nameless in-game. Because of limitations, Multi-Man Melee in SSF is a four-player match as opposed to the six-player match as it is in Melee. Matches are always played on.

In equivalancies, Melee ' s Fighting Wire Frames are unable to use special moves, which includes a third jump to recover and the inability to shoot projectiles. But given the simplistic, five attack moveset characters have in SSF, "Fighting Shadows" have no limitations and indeed have access to all the moveset available for the playable counterpart. This said, "Fighting Shadows" can actually use moves to recover other than jumping and they also have access to projectiles, but only if the playable counterpart is able. For example: a shadow will use its side attack to recover (as it makes Sonic hover a bit and propels it forward without even having to jump), while a shadow  will be able to shoot a variety of beams with all of its attacks. With these advantages, Multi-Man Melee is actually a bit more challenging in SSF than it is in Melee.

Endless Melee is replaced with the unlockable Burly-Brawl Melee, which works identically; the only difference is that player has to fight an endless team of "Fighting Shadows" which are always the same character.

Rewards

 * Clear 3-Minute Melee with any character, then beat him in a match
 * Complete 100-Man Melee with any character, then beat him in a match. There's an easier glitchy method especified below.
 * Burly Brawl Melee: Clear 3-Minute Melee with any character.

Interestingly enough, exploitation of the skip glitch shows that Cloud also can be unlocked by simply starting Burly-Brawl Melee and proceeding to use the glitch, which immediately leds to his "Challenger Approaching" screen. Playing it the normal way and getting a set record in this mode does not trigger in anyway Cloud's "Challeger Approaching" screen.

In Super Smash Flash 2
It has been confirmed through the official F.A.Q. and the Smash Flash DOJO!!! that Multi-Man mode is returning. Only Cruel mode is confirmed at the moment. The opponents that will be faced are yet to be revealed.