Did the Aztecs believe in the devil?

no they didn't

Answer:

The Aztecs were a polytheistic bunch with around a hundred gods.

They did not believe in the Christian devil (never having been exposed to Western culture until the arrival of the Spanish) but they did have many unpleasant gods. Even the "good" gods were tough to like, demanding as they did a diet of blood and human hearts. The "bad" gods were pretty close-up and personal in their relations with people. List provided below.