World 2 (Dr. Mario World)
From the Super Mario Wiki
World 2 is a desert world in Dr. Mario World. It introduces green viruses as part of the viruses mixed in its regular stages, replacing the yellow virus, and viruses encased in bubbles as hazards. The world introduces obtaining Virus Coins from defeating viruses over the marked area as a method of completion. The second area introduces viruses in cages where activating Lock Blocks exposes them. When an area is cleared, Spikes and Pokeys appear.