Wario Land 3: Part 21: The Grasslands (Green Chest)

The Grasslands is one of the three levels affected by Wario's Flute. The flute causes a giant snake to spawn from a huge jar; you can use the snake's head as a boost, but it can also get angry and burn Wario with a fire breath. The snake leads you inside a tree where you find the Green Key. You then dive underwater to reach a small cave that contains the Green Chest, which holds a Magic Wand that Wario must use before it can be activated.