WELL NOW, you're pretty much head and shoulders above me, so there's really not much i can offer; that tear/eye thing is particularly great. But, i'm going to try being like REALLY NITPICKY and find some things:
Noses: Nothing to mention, nice study.
Disturbing thing: The big thumb looks kinda like a wrinkly sausage, you've probably put a bit too many skin folds on places that aren't close to the joints. I do realize that this is a very surreal piece, though.
Mermaid: boooooooooooooooooooobs Hair is excellent, torso and tail are great with no particular flaws, but the arms look off, somehow. They kind of don't have a lot of depth. I get the impression that her left arm is supposed to be further away from the viewer, yet it appears longer and thicker than her right arm. Slightly awkward pose on the right arm as well; normally ones arms would hang a bit in front of ones body while at rest, while the mermaids arm seems to be on the same plane as the body, which, if you try it out yourself, is actually a fairly uncomfortable position. Definitely not one you'd want to intentionally hold if you could avoid it, anyways.
Single tear: Fucking excellent, not much else to say. The eyeball itself miiiiiiight come off as being not quite spherical due to the shading, but i'm not really sure about that postulate myself. Possibly because the entire eye in reality is a shiny thing, whereas this is more of a matte shading.
Late night drawing: THOSE HANDS MAN. Fun doodle, obviously done faster than some other things, but those hands and that bent upper arm catch my eye. In all fairness though, it's hard to make proper hands quickly, and you have demonstrated that you do know to do it.
Self-portrait: Hah, very nice! Super expressive drawing, the only thing that stands out in an awkward way is how you've chosen to draw your nose. It looks more like a... 3. Besides that, nothing bad to mention (for me, anyways).
Kraken: Very interesting way you've drawn the water, gives it a kind of mural feel. It clashes a bit with how you've drawn the tentacles though; they're drawn in a mostly realistic manner, whereas the water is highly stylized and the ship itself is more or less a silhouette (which does fit in). I'm sure you already know this, but in general, it's advisable to stick to one style (or at least not use too different ones) within the same drawing.