I shall have a go at critiquing.
The first image is pretty alright though I would seriously recommend you try not to shade with blacks. It's a very ugly way to colour a picture and might be appropriate depending on the environment, but that's not really how real life looks for the most part! If I look at my hand and REALLY analyse it, I can notice that it's not just a peach-olive colour and then a colour that's mixed with black. there's bits of green, purple, maybe a bit of red, that sort of thing.
To use one of my characters for example, Mike isn't actually a full-on grey colour. For the most part he's a blueish-turquoise grey and even the environment can alter that. Depending on the lighting, he could very well be a warmer grey and such, you just gotta experiment with colour theory and look at what the light source does to a character. You don't just light things up with whites and shade things with blacks.
http://danidraws.com...our-skin-tones/ Here's an example of skin tones!! Just to get the ball rolling, but man it is an understandable challenge but the sooner the black/shade/white/highlight habit can be kicked the better, you become a MUCH better artist without it.
Second image: The arm on our right looks way too short compared to the arm that's shooting the fireball, there doesn't seem to be a bend, it's just like the hand appears after the elbow. Also, is that white bit on the hand his palm? Because if so, then his hand is backwards :-[
Also the tail looks like it's coming from his back rather than.. his ass and stuff :-[ There's a kind of unrealistic way the tail looks, which I think is also relevant to the first picture. With the first image it just looks like a stiff bat rather than a fleshy part of an animal. And with the second image the bend just seems way too close that it makes me think the tail should snap, but maybe that's just me being picky.
Those are just a few things, I hope it all makes sense!!!
