A guide on how to complete The Crowned Beast shrine quest, found in Rabia Plain, southwest of the Divine Beast Vah Ruta. You will need to complete this shrine quest in order to access Mezza Lo Shrine.
How to Ride a Mountain Buck
Kass is chilling out in Rabia Plain, which you can easily paraglide to from Divine Beast Vah Ruta (if you have calmed it down) and then Paragliding across the river. You can see Kass playing accordion near another pedestal characteristic of a Shrine Quest puzzle.
Let Kass play the song of this region to give you the Shrine Quest. The key to the puzzle is finding a Mountain Buck and mounting it. While you cannot register non-horses to stables, many animals can be mounted and tamed. Mountain Bucks will take about 75% of a stamina wheel to tame, but will need a lot of stealth to sneak up on. If you have a photo, tune your Sheikah Slate sensor to find one. There should be one nearby grazing.
Once you have tamed the Mountain Buck, bring it to stand on top of the pedestal while you are riding on it. A cutscene will immediately play and the Mezza Lo Shrine will rise up from the ground, completing this Shrine Quest.