2D lava Monster:

My base sketch.

I found an appropriate background from google images and placed my sketch over the top on a second layer.

i blocked out the silhouette in a neutral tone, before adding a little depth with a basic highlight, but kept it relatively simple as i wasn't entirely sure how the following steps would obscure any highlights.

I added an FX layer with both inner glow and outer glow and went about painting in the streams of molten lava flowing between the rock formations.

Finnally i added a second FX layer with tweaked values of the two glow types for the flames crowning his head.