The only thing that I say would help the game is zombie respawn. Currently, you can keep one zombie in an area and then farm all the others for resources. If the zombies were to respawn in the area once the king moved past the gate you could prevent this
on level 18 go to the left of the second switch and you will fall to the second floor. Push the wall left and you will enter a secret area. + if you appreciate the excess of balls
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