WL3 AMB: Desert Ruins Green Chest 

This is a in-development Wario Land 3 romhack (titled Wario Land 3: Another Music Box) that aims to give every single level in the game a new layout with higher difficulty, along with more usage of lesser-used mechanics and reactions in the original game.
This is Desert Ruins' Green Chest. Flat Wario is actually pretty hard to fit into levels, which is why his first appearance is this late. Also the enemies that induce it suck too, because of the off-screen earthquakes.
(Also sorry if you saw this video get uploaded and then deleted, it was a recording of an older version of this chest.)