After all this time, it’s time to go back to the Nora lands. You’ll only be able to fast travel so close to the waypoint, so get as close as you can then it’s time to hoof it the rest of the way. Along the way there will be patrols of Corrupted Machines and Eclipse, so take them out as you get to them, until you get to the Embrace gate where there will be a couple of Corrupters patrolling.
Take them out and keep going, killing any patrols you come upon until you get to Mother’s Watch. There are two more Corrupters here, as well as a few Eclipse. Take them all down however you want. When they’re dead, head up the hill towards the strange noise that you can hear. There will be more Eclipse patrolling this path so take them out when you find them.
When you reach the top you’ll find a group of Eclipse being supported by a Corrupted Thunderjaw, which is not exactly an ideal situation. If you can rack up multiple arrows, do so with Tearblast and hit a disc launcher to start the fight, hopefully taking it off in the process. As soon as you start fighting, the Nora will come out of the mountain to help you, which means that you can focus on the Thunderjaw.
Your tactics are pretty much the same as if you were facing a regular Thunderjaw. Tear off the disc launchers then use them against it to do a good chunk of damage. Once you’ve done that, hopefully you’ll have blown off some of the armour that covers its heart. Again, if you can rack up multiple arrows, do so with something like Precision arrows and keep hitting the heart.
When it finally goes down, mop up the remaining Eclipse then talk to Varl. Once that’s done, head into the mountain. On your way to Teersa, if you’ve not already picked up the power cell here, take a right then head along to the section that has a locked door one way and an accessible vent the other. Go through the vent to find the power cell. When you’re ready, go talk to Teersa to trigger the cutscene.
Once inside, follow your waypoint and make sure to explore around and grab the datapoints as you go. Get to the locked door and let it scan you, then head into APOLLO. Follow your waypoint through the teaching room and into the next area, then activate the holotheatre. When the cutscene is over, head to the lift shaft and climb up then head back out of the facility. When the next cutscene is over, that’s this section complete. Before you leave on your next quest, make sure to talk to Teersa as you’ll find out Rost’s backstory