Cihuātlahtoāni Chicomecōātl of the Aztecan ponies; Queen of the Temple of Chicomoztec and Keeper of the Seven-Sided Chest. Her magic keeps the lands directly next to the San Palomino Desert fertile, but has a strict no-trespassing rule, lest you find yourself as her sacrifice. A strict ruler, she is worshipped as a god by her followers, living in peaceful isolation deep within her jungle.  
She appeared in “Summer Twinkle and The Temple of the Golden Sun” when Summer Twinkle attempted to steal the Seven-Sided Chest, thinking it the cause of local draughts. Despite fighting through the traps and guards, she found that the chest had in fact already been stolen, which was the cause. In an unusual fashion, the novel ended on a cliffhanger, suggesting a sequel where she would return the treasure to its rightful location.  
She makes a cameo appearance in the MLP:FiM episode “Stranger than Fan Fiction”. See if you can spot her!
 
This is a first draft of her snake design, which might be altered later.