Thanks for the review! I wanted to give the Warden/GM more than they needed so they could keep or discard as they saw fit.
You've found one of my cleverly disguised typos! There are Crystal WORMS and Iron BATS. So, entry 6 on the Encounters should be Crystal Worms. Originally, there were Iron Worms and no bats, but then the mine's ecology changed. Nice catch, and thanks for asking!