there is pillowshading on the tentacles. the white of the eye doesn't have enough contrast between the shades. The pupil is wrong, look up references of eyes from the side. the blue and green don't blend together at all, as if they were different parts of the eye. the blue is too saturated. the veins do not follow the pattern of natural veins, that's something else you shouldn't leave to imagination. Always use photographs to refer to when drawing forms you don't understand. the use of black outlines is too inconsistent, so it is distracting.
I was inspired in the Eye of Cthulhu. I am also a beginner pixel artist.