Puff Up

Puff Up is Jigglypuff's Final Smash. When used, Jigglypuff slowly inflates itself to a very large size, enough to almost entirely cover a small custom stage. While growing, enemies and items will be pushed away, dealing 18% damage. Once Jigglypuff reaches its full size, it shouts "Jiggloo!", which causes a massive push that will most likely KO any enemies too close to its body. Jigglypuff then quickly deflates.

While the move covers a very large range, it loses potency quickly on larger stages, and it has no effect on anything below Jigglypuff. Also, it will KO teammates even when Friendly Fire is off.

Origin
Puff Up is not an actual attack in the Pokémon games. Though, it is certainly similar to Jigglypuff's Expand move on some Pokémon cards.

Glitch

 * ''Main article: Puff Up glitch

There is also a glitch in the game where the terrain in some stages (mainly Bridge of Eldin) touches Jigglypuff and knocks it out of the move, yet it remains the same size it was when it was forced out of the Final Smash. If Yoshi (or Kirby with Yoshi's ability) uses his Egg Lay on Jigglypuff after this, or Jigglypuff picks up a Super Mushroom, its size doubles, allowing Jigglypuff to become the biggest character in the game. Its size resets when it uses the Final Smash again or dies.

Trophy Info
''Jigglypuff's Final Smash. It wills its body to get bigger and bigger and bigger. It can't move, and it can't attack--all it can do is get bigger while everyone else looks on. However, it's invulnerable, and it overpowers all attacks to gradually push its opponents off the screen. It's a very simple technique, but how it's used determines its effectiveness.''

Trivia

 * Jigglypuff's size before using the Final Smash affects the size it grows to. In giant mode, it grows to a size where only its face is visible on screen.
 * As a pun on its enormous size, this glitch Jigglypuff is often called "Bigglypuff", "Gigapuff" or "Gigalypuff" by fans. A gigantic Jigglypuff similar to Jigglypuff after using Puff Up was nicknamed "Bigglypuff" in the "The Ancient Puzzle of Pokémopolis" episode of the Pokémon anime.
 * If many characters get stuck between Jigglypuff and a wall at once (like the Ice-Climbers), the effects get slown down.
 * When the glitch is performed, Jigglypuff will still have the strength it had when it was normal sized. It'll also move very slowly, be unable to jump very high, and fall down slowly, all attributes equal to when it was its normal size. This proves that all the glitch does for Jigglypuff is change its size, as the game still acts as if it was its normal size.
 * The attack can be easily avoided by simply hanging off of any ledge. However, if Jigglypuff's foot is hanging over the ledge, then that character will still get pushed off.