He comands armies of thousands. His people love him. He has dominated and won dozens of wars. It's understandable that after all this stress, he has relaxed a little. And maybe gotten a little bit chubby.
All of the dragons listed below can be used to counter the Aztec Emperor dragon in fights, since all of them deal Critical (super effective) 2X damage against the Aztec Emperor dragon, but the Aztec Emperor dragon does not deal critical damage to any of these.