Indeed you have not followed the rules.
Leaving in your gallery but removing from the challenge, k.
I think Eggy is right.
But that aside, there's a few things that a bit awkward imho. For one, I think the square part near the snakes head where it curves is very weird looking, as well for the dark green colour on the right side of the mouth of the snake. I think that the colour of the snake is also a bit off, you're using a light green on the body but it doesn't really show up and rather blends in with the main green. You should make the differences between your colours more imho.
The lady is much better than the snake :)
I think you should re-read the requirements.
-The challenge explicitly states that you are to make a non-humanoid character, that is a character that does not have a torso that connects to a head, 2 arms and 2 legs. However, your character doesn't meet that requirement.
-Transparency is required. 
But other than that, it's not bad. Though the snake thing looks flat and I can see an almost sharp corner and jaggies...
EDIT: Also, after looking at the list of Green Lantern characters, you also appear to have made a sprite of an existing character, whereas you should've made your own.
My fault, because at first i think that it is non humanoid.