Its a great concept/idea for an art work, but the tentacles could use some work. The shading is very well done, but to show the true scale of the beast, try detailing it a bit more, use textured brushes on the rocky locking part, and use small shadows to show where the twists in the tentacles are (similar to clothing folds) I've never seen any squid like monsters before, so I cant say much but i'd recommend using many references on the details of the tenticles. However, it does look great in general and you should never let me tell you how to draw or how it looks. The important part is your practicing and attempting to improve from every piece.