Aquaria/Mithalas Cathedral

How to beat the six-eyed beam-monsters
While in energy form, shoot each of the six eyes so that they are all open at once. The monster will then spin, likely spraying you with a few waves of laser fire. Then you will see a brain-like structure grow out of the creature's bottom. This spot is vulnerable; shoot it repeatedly to win.

You will need to do this three times to access the Cathedral basement.