From the Super Mario Wiki
Grassy Greens is the first world Mario goes to in Mario Pinball Land. As its name implies, the land is covered in grass and possesses a farm-like setting (with the farm tune to boot), along with classic enemies like Goombas and Koopas, beehives with Bumblers, and a big windmill (where Toad's Tent was located nearby). Inside the windmill, Mario fights what would appear to be a deformed version of Petey Piranha and takes his Star Key to move on.
The entrance to Grassy Greens.
The area with the windmill.
Mario's battle against Petey.
- ^ Mario Pinball Land instruction booklet, page 20.