The creature depicted above is called the ahuizotl. In Aztec mythology, it lived in lake Texcoco, and was the guardian of the lake & the fish that dwelt within. The hand on the end of it's tail was supposedly used to drag fishermen, or anyone else, that got too close to the water.
The figure you see on the left is Aztec emperor, Ahuizotl. Much like his namesake, the ahuizotl creature that supposedly lived in lake Texcoco, he was swift and aggresive in his decisions.