There's probably something symbolic about the tendencies of a villain to turn into a snake. In the West there is a strong established symbolism for snakes from The Bible (most famously the serpent in the Garden of Eden, although some translators believe that the original text may have indicated that the creature was closer to a dragon than a snake), Norse Mythology, and there's Orochi in Japanese mythology. Adding onto this, there is the fact that when walking in the wild, it's generally not a good idea to stop and pet a snake. Examples of Scaled Up include: