WOW!!! You've really improved, and really quickly!! Good for you friend! The creature design is reallly really cool, I love this concept. Unfortunately it looks better when its smaller than when I view it full size, as the linework seems a little sloppy. That's alright though, cause I can't stop looking at that bad ass bill!
Don't be afraid to add the color of your atmosphere to your subject. Even if the platypus is glowing, two things would happen;
1. The farther away something is, the more muted and the more its going to blend into your background. You could really push the illusion of depth by shading in some of that back tail with the beautiful blue you've chosen.
2. Light reflects, specially in water! I would check out some underwater glowy creatures to get a better idea here;
http://www.bluezooaquatics.com/images/promos/mazel_condylactis.jpg
http://www.danintranet.org/media/adimg/4437.jpg
Keep it up bro! You're almost there!
