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 can't change colors, so it is pretty difficult to tell which character is and who isn't on the team.
In Super Smash Flash 2
In Super Smash Flash 2, the player can choose who is and who isn't on the team. Starting from demo version 0.4, the characters change color according to the team they are on. They also have Team Damage, which allows attacking other characters on player's team. Even though Team Damage is on, you can't do a Battle with one team. It is possible to share stock by pressing the pause button when the player runs out of lives. The result is the player gets revived with one life, at the cost of a teammate's life. This doesn't work if the teammate(s) only has one life.