You will encounter monsters in the shape of bats, some are easy to kill and some are harder.
The depper you get in the mine the tougher they get. Fight well and you will get revarded in gold achievements and perks.
The game has its own website Batified.se where you can kill bats to get the highest mission score.
You can submit your highscore to the batified leaderboard and see it on Batified.se.