Great squid are a type of giant squid. A great squid killed some of the pirates that had kidnapped Gwydion when he was escaping Llewdor, it is believed it could have been the great squid-like being Cthulhu. A great squid can be found near Mordack's Island, and tries to attack anyone trying to swim away from the island.
Behind the scenesEditGiant squids (or perhaps giant octupuses) are shown on some of the maps in the King's Quest Companion. Some of the images of giant cephalopods might be giant octopuses, but they haven't yet been specifically referenced.
The squid perhaps a 'kraken' is called 'killer' in the file, and death scene refers to "Saying hello to "Davy Jones".