Mysteries of the deep Trophy in Radio Squid
Mysteries of the deep
Beat a boss on floor 2.
How to unlock Mysteries of the deep
Again, there are multiple bosses available on the second floor. Find and kill any to get this trophy (see Got a Bite). The one I did, on the top path, was a clam boss. This boss also shoots bubble and droplet-shaped bullets in all 4 directions and also switches paths from horizontal to vertical every so often.