Jigglypuff

Jigglypuff, known in Japan as Purin is a pink balloon Pokémon who is known for singing people to sleep in the  anime and looks like a puffball, similar to Kirby. Apart a minor cameo in A Super Mario World, it is also an unlockable character in Super Smash Flash and a starter character in Super Smash Flash 2.

Character description
Jigglypuff first appears as one of the 151 species of Pokémon in, and appears in all versions following it. Despite not being a lead character in the Pokémon franchise, Jigglypuff was selected to appear in the  series due to its similarities to Kirby, which allowed the staff to reuse the model and many animations as a base for Jigglypuff.

As mentioned above, Jigglypuff is similar to Kirby in appearance; however, Jigglypuff has larger eyes, thinner limbs, and large, triangular ears, as well as a curled tuft of hair on on its head. This somewhat feminine appearance has led to many players to refer to Jigglypuff as "she". Within the Pokémon world, there are both male and female Jigglypuff, and females are more common than males, but the Super Smash Bros. character is always referred to as "it".

The Pokédex provides additional biological info about the Jigglypuff species: After it mesmerizes its foe with its large, round eyes, it sings its lullaby until the foe sleeps, and does not stop to breathe until the foe is fully asleep; it can perform longer with its single breath if it inflates its body with air beforehand. Its vocal chords can freely adjust the wavelength of its voice, and it sings at precisely the right wavelength to make its foes most drowsy. The sound waves of its singing voice match the brain waves of someone in a deep sleep. Nothing can avoid falling asleep after hearing a Jigglypuff's song, but some are more naturally resistant to the effects than others and take much longer to sleep. This effectively endangers a singing Jigglypuff's life because it cannot breathe.

In A Super Mario World
Jigglypuff makes a minor cameo during the bloopers reel of Episode 2 of the A Super Mario World series. When Sonic tries to transform into Super Sonic, he fails and transforms into Jigglypuff instead, much to his dismay. It just takes Mario one hit to take out Jigglypuff.

In Super Smash Flash
Jigglypuff appeared in Super Smash Flash as an unlockable character who could be available by completing Adventure mode in any difficulty with any character.

In Super Smash Flash 2
Jigglypuff is a secret character in demo v0.9a while being a starter character in the full game. During the APEX 2013 Livestream, it was revealed to be a character added in the 0.9 demo. Jigglypuff's sprite design is based on its appearance in the main Super Smash Bros. games. Its move set is taken directly from the Super Smash Bros. games.

Trivia

 * Jigglypuff uses the same sprites for its appearances in A Super Mario World and Super Smash Flash.