When performed, Jigglypuff inflates slowly to an extremely large size, enough to cover the entire length of Final Destination, pushing away opponents that make contact with it while inflating. Once at full size, it shouts "Jiggly!", dealing about 15% damage and extremely high knockback to any opponents nearby, which may result in a one-hit KO with the right conditions. After this, Jigglypuff quickly shrinks back to normal size, ending the move.
Although Puff Up does not appear in any of the Pokémon games, it appears to be based on Jigglypuff's classification as the "Balloon Pokémon", with the Pokédex stating it can inflate its balloon-like body. This ability is shown in other Pokémon media such as the anime, in which it often puffs up when angered. Puff Up is also similar to the Dynamaxing ability that later appeared in Pokémon Sword and Shield, which Jigglypuff can use as of The Isle of Armor expansion.