This guide shows how to open the locked chest in Guau Guau Island in Far Cry 6. You will find a locked chest in Guau Guau Island (Isla Santuario) at the location shown in the picture below.
To open the locked chest, you will need the ‘Mysterious Key’. You will get this key as a reward for completing Who’s a Good Boy? and Fetch Quest Yaran Stories, which are a side-quest chain that gets you Chorizo dog as a pet. The player must complete the “Meet the Monteros” Main Story Quest (Operation) in Far Cry 6 to start the “Who’s a Good Boy?” side-quest. To start the side quest, the player needs to visit Costa del Mar sub-region in Madrugada and pet with the quest giver (Chorizo). Click here to see the complete walkthrough of Chorizo quest chain.
F*ck Anton Unique Weapon
Use Mysterious Key to open the chest in Guau Guau Island and get F*ck Anton Rifle.