Frank Frazetta is a master illustrator who helped popularize Sci/Fi and Fantasy Art. One of his most popular character designs that has been repeated in countless movies, book covers, and video games is his Death Dealer.
Underneath his wonderful paintings were amazing drawings as a solid foundation.
A fundamental understanding of good anatomy so that he could make the fantastical believable, and the impossible feel real.
As he inspired Hollywood, he was also inspired by it. Directors such as Alfred Hitchcock who hid the creatures in his films till the big reveal knew that there was nothing scarier than theatre of the mind.
Even with a limited color palette, Frazetta had power through composition, value, and gesture. Look at this monochromatic piece of Icarus.
All fantasy work has to have a basis in reality. There has to be a logic to why it works. That logic acts as a set up for why the fantastical is visually digestible to the eyes and mind.
What an expert use of contrast and framing of the environment to make the action the focal point and accentuate the stars of the show... the warrior and snake.