what did you use to create Demon with?

Pretty nice, but the proportions need some work.

+7

The proportions are supposed to be that way with him... He's not human you know... If he was, it would be totally different for him.

I understand that he is not human, and that you can, maybe even should, make the anatomy different. But there are some anatomical laws you should stick to, even when designing a demon such as this. In example, the arms have muscles, yes? So they shouldn't be flat in the front. And making the hips a little wider would give him better balance. His mid could still be very slim.
When it comes to the pose, I think it would look more natural if he held his hands so that they are viewn from the side, when he stands in front view.When you hold your hands relaxed hanging down along the side, the palms will naturally face towards your body, and not forward. It looks very unrelaxed the way it is now, and since the rest of him seems to be relaxed, so should the hands. At least that's my opinion. If you want him to hold the hands forcefully, almost angry, with palms up like this, you must make the elbows bend in order to prevent the relaxed look.

With that said, it's still a nice model. Was it made with Zbrush...? Nice back-muscles.