????? is the event #51 in Super Smash Flash 2. It is the last event in the game, and can only be played if the player has obtained A rank or higher in every other event.
In order to clear this event, the player must use a character of his choice to defeat two Master Hands. Both Master Hands have 500 health points, and the player has 1 stock. Additionally, there is no delay between the Hands' attacks. Fireworks will spawn periodically, and the player can use them to damage the Master Hands. However, the fireworks can be hit by the Hands themselves, in which case they'll deal damage to the player and the Hands. The Master Hands briefly freeze whenever they are hit by Fireworks, and they can even damage each other with their own attacks. There is no time limit for this event, but the ranking the player gets is based on how much time it takes him/her to defeat the two Hands.
The second Master Hand is most likely supposed to represent Crazy Hand.
In this event the second Master Hand's laser attack will only deal damage at the start of the lasers, which are also bugged.
It is possible to get KO'd and fail the event even if the Hands have been defeated.