From the Super Mario Wiki
Piranhacopter is Piranha Plant's up special in Super Smash Bros. Ultimate. When the move is used Piranha Plant spins its leaves in a circle making it fly upwards, and while Piranha Plant is flying the player can move it horizontally. After the move is over Piranha Plant falls to the ground and cannot attack until it touches the ground. If an opponent touches Piranha Plant while it is using this attack, the opponent will take damage from its leaves while being carried upwards until the end of the attack where the fighter is launched from the attack.