Maybe use the Burn Tool (assuming you used Photoshop) along the dragons back underneath the characters to give them some shadows under them. It'll make it look less flat.
With the beach pictures you might want to change the feet to make it appear that they are in sand rather than on a completely flat surface. The fishing one you should remove the drop shadow.
Other than the techincal issues they are well placed and awesome subjects.
EDI: Cause I'm ANAL. The tiger's shadow should be stretch outside of the frame since it's leaping in. The lens flare is also out of place. Unless that's a very shiny piece of glass there the tiger is blocking the water where you had the lens flare in the original picture.
I'm sorry if this is coming off as too much critism. I can see what your trying to do and I just want to help you out.
DOUBLE EDIT: god damn i've got OCD or something....the crab shadow is out of position, the feet don't match up. OK I'm done! You can ignor me from here on out.