Board Thread:Plants vs. Zombies 2/@comment-35431153-20180501230732/@comment-26127523-20180503001859

Sounds like the "Veteran Levels", which got added after a somewhat recent update. So you get another Zomboss battle at the end! Those levels are indeed supposed to be more tough, requiring a combo of more skill, premium plants, or leveled up plants.

If you're referring to only the world in general, you can use the jalapeno difficulty rating when on the browsing worlds menu