Mamono Sweeper might require some explanation first. Like Minesweeper, the numbers indicate how many monsters are in the surrounding squares. Instead of simply marking mines, however, the aim is to kill the monsters.
You begin at level 1. The legend at the bottom of the screen tells you what level each monster is: cyan is level 1, red is level 2, etc. You can kill any monster of your level (or lower) just by clicking on it. As you kill monsters, you gain XP until you level up and are able to kill higher levels monsters.
Make sense? Now, go play!
Mamono Sweeper [Hojamaka]