You need kill all creepers to save the world!(and I made this game so ezzzzzzzzzzzzzzz)and defeat the easiest boss in the world!(its my first game don't spam me...
you should totally make new worlds. since you technically did an earth level and this is based on mine-craft. you should use the end and nether in mine-craft with the basic mobs as the enemy's or try to make up some new enemy's and worlds. Try playing some other games and use what you see as your canvas and change a character up to make it look like an enemy. This should give you some ideas. but its just an idea so theirs no need to take it seriously.