Before completion: Carefully study the Itzel fighting style and then challenge their enemy's champion to claim a valuable daily prize.
After completion: You can now fight Mayatl the Fierce by speaking to the Itzel bladedancer outside the Jaka Itzel village. Defeating this champion gives you access to a reward chest once per day.
— In-game description
Champion Mayatl the Fierce is located on a top of the hill west from Temple of Ameyalli. You need to speak to Itzel Bladedancer to summon him.