This is another one you pick up at Mother’s Crown, speak to Den to get it. You’ll need to travel to Devil’s Thirst to find the rest of his hunting party that have been separated from him. Once you’re in the Ruins, head for the waypoint, then scan with your Focus once you arrive and investigate the corrupted Watcher. You’ll pick up some tracks to follow, highlight them and follow. When you get to where they were leading, you’ll be confronted by two patrolling Sawtooths in an enclosed environment that you’ll have to get rid of. This is no easy task, but there are ways to make it easier. If you’ve been to Cauldron Sigma and got the Override codes for Sawtooths, you can just stealth up to one of them and Override it. It will then leap on its companion and do a good amount of your work for you.
If you don’t have that option, your tripcaster plus some well placed fire arrows to the Blaze canister on its underside are your best ticket to a simpler victory. When the Sawtooths are down, the other hunters will come down from their hiding place. Then it’s just a case of talking to Den again to get your reward.