This sidequest is unlocked after you finish the Deadliest Game Errand. Ahsis and Talanah have gone off to confront the legendary Thunderjaw Red Maw, and it’s up to you to find them and help them defeat it. Follow your quest marker into the jungle until you reach a group of enemy hunters who have captured Talanah. Take them all out to free her.
Once they’re down, talk to Talanah who’ll inform you that Ahsis hired the hunters to hold her captive while he took a crack at killing Red Maw all on his own. Follow her until she loses the trail, then use your Focus to find the tracks and follow them instead. After finding a series of signs that point to Ahsis and Red Maw fighting, you’ll find them battling in a hollow. Ahsis will be taken down, and you and Talanah must bring the Machine down yourselves.
Red Maw is basically a regular Thunderjaw on steroids. He only has one Disc launcher, so your usual avenue for dealing damage to him is truncated, and he has higher base health than a standard Thunderjaw. Your best bet is to use the Disc launcher anyway then start throwing down blast wires and using Tearblast and Hardpoint arrows to peal off his various weapons and weakpoints. Once his armour is mostly gone, use Precision arrows on his heart and he should go down soon enough.
When he goes down, loot him for some killer prizes then talk to Talanah. After that conversation is done, talk to Ahsis for the last time then head back to the Hunter’s Lodge. When you get there, talk to Talanah again to complete the quest, and this quest chain.