Designing imaginary creatures takes more than just drawing or painting skills; good creatures, to my mind, require imagination and originality, or they seem like everybody else’s creatures.
Mike Corriero does terrific creatures.
Corriero is a freelance concept artist and illustrator for the gaming and film industries. His clients include Radical Entertainment/Vivendi Universal Games, Challenge Games, Liquid Development, Piazo Publishing and Hasbro Inc. You can find a list of some of the projects he’s worked on, as well as publications in which his work has been featured in the Resume on his website, and the bio on CGHub, which also features a quickly accessed gallery of his work.
In the gallery on his own website, there are sections for Sketches, and finished Illustration and Concept art. When viewing the images, there is an “Enlarge” button above the main image that launches a much larger version (in most cases) in a new window.
There you can find his imaginative creatures and monsters, with multiple appendages, wild textures and strange shapes, and often painted with a touch for incorporating a range of colors into his renderings. You can also find environments and other illustrations.
You can find more information about his work and projects on his blog.