The creature doesn't look backlit, and the shadow should conform to the contours of the steps, as well as have more edge blur and maybe a bit less opacity.

Thank you for the help.

Good work with the portal.
The background looks unconvincing. Folks here use vegetation rocks or premade background to make the environnement look realistic.
Use imageafter.com and sxc.hu to find blendable stock.

It looks ok, but I think you should have used other kind of plants or background as greymval says... and the foreground is not convincing for your kind of work. The alien looks cool. The rocks.... look ok. Good luck author.