Not bad for a start!

Brick: either use the black outline on the whole piece, or not at all. Could use a lot more contrast, esp highlights; and could use hue shift in highlights / shadows.

Monster: it's not pillowshaded, but not so well shaded either.
Look well at the ref: the sunlight from above-behind-left is much stronger than you made it, it makes strong highlights and the arm casts a shadow; there is a bluish diffuse light from above-right-front (light from the blue sky), esp on the face and right arm; there is green reflected light from below left, and neutral reflected light from front.
4 light sources! Each has its color and contrast, each casts specific shadows.
Look at the mouth, there is shading inside, distinct reflections on teeth...

Lines could be cleaned too, again look at ref. How arms and legs are attached, crotch, mouth. The feel is more soft, rounded than yours.

Then you might try some texture, that won't be easy.