From the Super Mario Wiki
Jet Pots are rabbit shaped power-ups that turn Wario into Jet Wario in Wario Land: Super Mario Land 3. When Wario gets one, thrusters appear on a helmet, allowing him flight. Since Wario is so heavy, he glides down slowly but can still fly until he hits ground. While wearing this pot, Wario's jumping power is increased as well as his walking speed.