There’s a quest in Exalted Plains given by Ithiren on the Dalish Camp. He seeks your help in returning the Golden Halla. The Golden Halla can be easily found since its indicated in the map after you’ve accepted the quest.
It’s just like a normal Halla where you can actually select it and kill. But what happens when you kill it and not return it back to the camp? Well, the Golden Halla drops a guaranteed Golden Halla Hide which has the description of: Enter stealth when not attacking during combat. However, when you go to the crafting table and select it, it will have the correct and working description: 10% chance to cast Fade Cloak on hit.
If you’re wondering if you still get to fill the Dalish Favor to 100% even if you’ve killed the Halla, then yes, you’ll still be able to complete the By The Grace of The Dalish quest even if you’ve killed the Golden Halla, as long as you fulfill the other requests on the Dalish camp.
If you decide to return the Golden Halla to the camp, just ride your mount to make it faster and herd him back to the direction of the camp.