Minecraft wiki entry for Nether_Update, associated text: "This concept was made as we started talking about introducing huge nether warts in the Nether. This eventually led to us deciding to turn it into its own biome." – Johan Aronson, art director.
"We wanted to extend the palette in the Nether to enhance the feeling that you're not in the Overworld anymore. This was an experiment to find a suitable, contrasting palette to the original Nether setting." – Johan Aronson, art director.
Artwork by Johan Aronson, art director.
Concept art of an early design of the strider.
Concept art of the strider.