The Mu Saddle can be found inside a Wooden Chest within treasure rooms located in the Deep Mine, or the Island Reef, or for sale on Jimmy's Boat (a random rotation).
Equip the mu saddle on a Mu or Wary Mu and ride it. Walk up to the mu and select "Drive".
Once saddles are equipped, it cannot be unequipped from the mu unless the mu is killed by an aggressive animal.
Placing the Mu Saddle on to a Mu or Wary Mu creates a type of vehicle that can be ridden. As an animal it cannot be broken down to be put into the player's inventory. Though using a Mu Whistle will teleport the closest saddled Mu/Wary Mu to the player on the island. Aa a passive/neutral animal it can be attacked and killed by aggressive animals, where the saddled will be dropped. Feed Quandongs to recover health. They will sleep inside an Animal Stall.