-The blue space near the legs of the character looks very out of place. and same goes for the white space. It's too bright and plain.

oops 

-The monster can use a bit of a make-up since it's really difficult to see and make out at first glance.

ah yes! I had no idea how to fix this, but then flashbulb happened, thus, now i have attempted to fix it

The "spotlight" should bounce around a bit more light on the environment? (I'm not sure, though. Just saying what I think.)

i believe not, the spotlight is facing the viewer (although if this was real life, it wouldn't), therefore, the only light it goes into is your face, which if i am correct, is outside the drawing 

I think the ground can also benefit from small props and irregularities.

but it has all the little rocks and grass x) is that not enough? if somebody else disagrees, i will try 

-The shading on the trees and the monster seems very conservative.

the trees: low importance, low detail
the monster: as far as i know, ink and inky things aren't very receptive to light, only having a slight change, and then the spotlights (which i went overboard with)

It's done really well though, it's leagues better than what I can do right now.

thank you
now for the slight revision

added a backlight, filled the white space with some trees, fixed the bluespace
if anybody wants a version without characters, for whatever reason here it is