Background characters are minor characters in the Super Smash Flash series that make cameo appearances in their corresponding home stages, normally without interfering in the battles. As such, background characters should not be confused with stage hazards.
With the severely limited stage selection of Super Smash Flash, the game only had one background character in its eight stages, but Super Smash Flash 2 includes many background characters in its large and growing list of stages.
In Super Smash Flash
- Whispy Woods appears on Dream Land's background. Unlike his appearance in the original Super Smash Bros., he is merely a cosmetic addition and does not blow wind.
In Super Smash Flash 2
- Waiting Room has multiple background characters that appear in its several designs.
- On Waiting Room's normal variant, Sandbags appears on both couches. The one on the left couch stands and occasionally blinks, and the one on the right couch lies down and sleeps on it. There is also a mini Sandbag sitting next to the one on the left couch and there is another Sandbag leaning against the right couch wearing a pair of sunglasses.
- On Waiting Room's Halloween theme, a Boo can be seen floating above the left couch. There is a dizzy Sandbag spinning next to the left couch. ＣＬＥＯＤＢＯＴ also appears for a brief moment on the televisions as they transition from a spooky face to the SSF2 logo.
- On Waiting Room's Christmas theme, Sandbag is wearing a Santa hat and can be seen jumping happily on the left couch. There are two mini Sandbags jumping on the right couch also wearing Santa hats.
- Lava Bubbles jump in from lava in the back of Bowser's Castle.
- On Galaxy Tours, a few Lumas are seen soaring around the Starship Mario. The Luma known as Lubba can also be seen in front of the steering wheel of the ship.
- On Mushroom Kingdom, Koopa Troopas are walking back and forth on the platforms in the background. Also, a Buzzy Beetle is bouncing endlessly on a spring in the background.
- Multiple Mini-Necky flocks appear on Jungle Hijinx, flying from one side of the screen to the other.
- Pak E. Derm walks back and forth behind the trees on Yoshi's Story.
- Jimmy T. appears during the Taunt! microgame on WarioWare, Inc..
- On Crateria, a Geemer appears walking around in a tunnel, in the bottom platform's right (from the viewer perspective).
- King Dedede can be seen flying across Dream Land in the background, from the left side to the right. A group of three Bronto Burts can also occasionally be seen flying in a wavy pattern in the background, from the right side to the left.
- Magnemite and Beldum can be seen in the background during the Steel transformation of Pokémon Colosseum. Dewpider and Kakuna can be seen in the background of the Bug transformation.
- Butterfree and Moltres can occasionally be seen flying across Saffron City in the background.
- Giygas appears all throughout the foreground and background of Devil's Machine, moving endlessly across the stage.
- A sleeping Red Bulborb lies in the back of Distant Planet. A Cloaking Burrow-nit can also be seen left to the Red Bublorb, but far behind it.
- Captain Viridian is seen on Nintendo 3DS stage's screen during the VVVVVV game, changing the stage's gravity.
- The Eggrobo can be spotted flying on Sky Sanctuary Zone's background from one side to the other.
- The four ghosts — Blinky, Pinky, Inky, and Clyde — roam across the maze on PAC-MAZE.
- In Chaos Shrine, a huge flock of bats are seen flying in the upper part of the stage. The four fiends — Tiamat, the Kraken, the Lich, and Marilith — float by in the background. They do not move at all other than scrolling from side to side.
- Fairy Glade has multiple background characters.
- Globox stands next to the bouncy mushroom and simply watches the fight.
- Popolopoïs fly around the stage and rest on the giant tree.
- Small mushrooms stack on top of each other, helicopter bombs fly from one side of the stage to the other, and a warship flies off in the distance.
- Vegeta IV, Trunks, and Son Gohan fly across Planet Namek from right to left at high speed.
- On Thousand Sunny, members of the Straw Hat Pirate Crew can be seen in the background. Except for Zoro, they all cheer upon a KO being scored.
- Roronoa Zoro is seen sleeping with his three swords alongside him.
- Nami stares at a piece of paper, while sometimes looking at the screen.
- Sanji is watching the fight while smoking a cigarette.
- Franky watches the fight from the left side of the ship’s deck.
- Nico Robin is seen reading a book on one of the staircases.
- Usopp is cheering for the fighters by raising his fists in a pattern.
- Brook plays music from his guitar on the staircase's railing.
- Tony Tony Chopper simply idles while watching the fight.
- Jinbe watches the fight from the right side of the ship’s deck while his arms are crossed.
- Hidden Leaf Village has multiple background characters.
- Chōji Akimichi is seen sitting at the Ichuraku Ramen bar, eating a lot of ramen.
- Gaara is seen left to the bar, bending some sand.
- Hinata Hyūga will occasionally lean out from the right side of the bar.
- Itachi Uchiha teleports in to the plateau on the background, to later teleport out.
- Rock Lee is seen doing one-handed push-ups in front of a flower shop.
- Shikamaru Nara can be seen snoozing on the bar's rooftop.