This is one of the attacks that Wario can perform (only in Smash). Wario can get gassy if he eats an object (or character) with his neutral special. He builds up gas until he flashes yellow to indicate the attack is charged at full power. Then he farts, unleashing a nauseous blast of devastatingly stinky yellow-ish smoke. Uncharged, the attack Wario makes is nothing but a small puny fart which trips, only to be followed by a quick "Sorry." or " 'Scuse me.". This attack is in Super Smash Bros. Brawl and all subsequent entries.
An uncharged Wario Waft from Super Smash Bros. Brawl