The flipper comes from Balloon Fight. In Balloon Fight, if a player bumps into a flipper, it starts to spin. If a player or enemies hits the flipper while it's spinning, the player temporarily flies out of control. After awhile, the flipper stops spinning. In Melee, the flipper can be picked up and thrown. When it is thrown, it stops in mid air. When a player attacks the flipper, it starts to spin. If a player is to touch the flipper while it's spinning, it knocks the player away. Also, the flipper slowly stops spinning after a certain period of time. 
After the Flipper travels a certain distance, it stops in midair. When hit, it spins either slowly or quickly (depending on either the speed of someone who has contacted it, or the strength of the attack), blocking passage and causing light (though generally repeated) damage when touched. Aside from causing general havoc in a fray, they can also be placed strategically at integral locations, such as ledges or against walls. This will prevent opponents from recovering, or not allow them to pass through certain points. The downfalls of this item are that it can be avoided with relative ease and has a relatively short duration on the field.
When used on moving stages (such as Big Blue, Rainbow Cruise, Poké Floats, etc.), the flipper will continue to move with the background instead of remaining stationary. This is most apparent on Big Blue, where the flipper hangs still for a split-second, then races off screen as the Falcon Flyer and racers speed away from it.
In Melee, the Flipper seemed to have replaced the Bumper from the original Super Smash Bros., as their usages and effects are quite similar, and the latter item did not return. The Bumper's return and Flipper's absence in Brawl further supports this, especially as the Bumper's new ability to be set in midair is identical to the Flipper's. Furthermore, when Masahiro Sakurai revealed the return of the Bumper for Super Smash Bros. 4, he stated "This also means there will be no Flippers," an official confirmation that the items were intended to fill the same niche and not appear in the same game together.
In Ultimate, Flippers once again appear as hazards on the Balloon Fight stage.
The hitbox of a set Flipper uses a unique knockback angle of 362, which is not used by anything else and has never reappeared in any later game. Its behaviour is to knock the victim away from the hitbox based on the direction between the point of impact and the center of the damaged hurtbox. Because these factors can be difficult for players to perceive, especially if the Flipper is rotating quickly, it can appear like this angle is fairly random. But in general, this means that dropping onto a Flipper from above will try to knock the character upward, while jumping into one from below will try to knock back downward.
Made famous as an unpredictable obstacle in Balloon Fight, the Flipper stops and hangs in midair when thrown. Any character who comes in contact with the bumper-balls on its ends will be knocked away as the Flipper spins wildly. Flippers can be a bit irksome: in Balloon Fight they caused accidents to friends and foes alike.