From the Super Mario Wiki
Garlic, Wario's favorite food, is a common item found in the Wario series.
In Wario Land: Super Mario Land 3, a type of Garlic power-up called the Garlic Pot appears. It turns Small Wario into normal Wario, and normal Wario into Bull Wario. In Wario Land 3, Garlic is one of the treasures that Wario has to collect. It is found in the Tower of Revival. Wario gains access to it by opening the Blue Snake door. It allows him to break solid blocks.
In WarioWare: Touched!, Wario eats a Nasty Garlic in Wario-Man's intro cutscene and transforms into Wario-Man. After the microgames are beaten for the first time, the Nasty Garlic will then appear on the main selection screen so that Wario can turn back into Wario-Man at any time.
In Wario Land: Shake It! Garlic makes a reappearance. Garlic can be obtained by shaking enemies and heal one heart of Wario's life meter. Occasionally, an enemy releases a big Garlic, which heals three hearts of Wario's life meter.