Greenhorn Forest

From the Super Mario Wiki

Greenhorn Forest is a forest that Wario had to go through in Wario World and the first level in the game. Being the first level, it is very easy, and all the items, like the five Spritelings, the eight pieces of the first Mr. Wario's Golden Statue, and the eight Wario's Treasures are relativly easy to find. The whole level is, pretty much, a tutorial.

Enemies here include Magons, Clubosaurs, Cractyls, and one Ankiron.

Greenfist is the boss of this level.

All of Wario's Treasures in this area are precious stones.

Areas in Wario World
Excitement Central
Greenhorn Forest | Greenhorn Ruins
Spooktastic World
Horror Manor | Wonky Circus
Thrillsville
Shivering Mountains | Beanstalk Way
Sparkle Land
Mirror Mansion | Pecan Sands