In Super Smash Flash, the player has the option to do a 2 on 2 match, 1 on 3 match, 2 vs 1 vs 1 match, and 1 vs 1 vs 2 match. Unlike the official Super Smash Bros. games, the characters cannot change colors, so it is pretty difficult to tell which character is and is not on each team.
In Super Smash Flash 2
In Super Smash Flash 2, the player can choose who is and who is not on each team. Starting from demo version 0.4, the characters change color according to the team they are on. They also have an optional rule called "Team Damage", which allows players to attack other players on their own teams. Even when Team Damage is on, you cannot do a Battle with one team. It is possible to share stocks by pressing the pause button when the player runs out of stocks. The result is the player gets revived with one stock, at the cost of a teammate's stock. This does not work if the teammate(s) only has one stock.