This is the fourth world of this game, New zombies appear after you complete a level and some levels are getting more challenging. Remember, if you defeat all of the zombies in the final wave, you can collect the trophy to complete the stage now, Start levels 1-10 and after you complete this whole world, then customize it and remix it or play a different world or a level if you want to.
Note, This project sometimes lag after you are playing each level.
