Thunder Island

From Mario - Wiki on Neoseeker

This level is a tiny island in the ocean, it has no electric fences so if a player hits the side they fall of for a short period of time. The wind blows a lot and obstacles such as cows may hit you causing you to fall of the stadium. The wind can also move the ball about, so keep your eye on the ball! Use the level to your advantage. When enemy players fall of, go in for your shot.