Once you’ve cleared the anomalies from a biome in Solar Ash, its guardian awakens. These massive bosses, called Remnants, are the final challenge before you can move on, so you have no choice about taking them down. The game’s second boss, the Forgotten Thresher, patrols the Broken Capital. Here’s how to bring it from the rooftops down to the city streets.
Step one, you need to actually mount the monster. You don’t need to ascend to the rooftops to do this — just look for a grapple point attached to one of its long fins. Grab that, and you’ll be hoisted up onto its long body. From here, you need to clear each successive weak point until Rei plunges her blade into the core of the beast. While the weak point pattern varies with each round (there are three total), the path will send you to the end of the Thresher’s tail before turning back toward the head each time, so be aware of that recurring factor.
Some of the platelets on the boss’s body will disappear before round two, so be aware that you’ll need to jump over the sticky black goo or be stopped in your tracks — and you will get burned if you’re standing in the gunk when the timer runs out. In round three, this goo gets super-heated, resulting in an instant death if you touch it, starting the round over.
That’s the structure of the boss fight. Some trial and error is certainly OK, if not expected, when taking down the Forgotten Thresher. Remember that you can always use Rei’s Suit to give yourself a quicker Timeslip cooldown if you need to be more precise with your jumping.