|Reality||Mirror Worlds||Space Eagle|
Utopia 4-21 is the twenty-first level of Utopia.
Three stars can be problematic for some. The higher pigs can be tricky.
Send Orange Bird near the edge of the atmosphere, having him fall between the first two towers. Managing to clear the level with a single bird will pretty much guarantee three stars, though combining more birds with more destruction can reach the threshold as well.