In the real world, squid aren't quite the mystery they used to be (I remember when the giant squid arriving at the Smithsonian was big news). But they still suggest watery depths we will never fully know. And anything that can tussle with a sperm whale deserves respect.
A standoff between treasure hunters and merfolk in a sunken city goes bad. It gets worse when a giant squid, drawn by the commotion, begins attacking both groups indiscriminately.
A minor artifact found in a skum lair is cursed. As long as it is carried, schools of squid will attack the bearer any time she enters salt water.
Food is a powerful teaching tool. A particularly cunning giant squid has learned a trick: it picks clean one vessel, then attaches itself by its suckers to the keel and waits. When the rescue ship arrives to look for survivors, it attacks them, too.
—Pathfinder Bestiary 259