On my YouTube channel I've created gameplay walkthrough videos covering Chapter 4 of this game.
This chapter has us going with Maya to the lighthouse. Follow Maya along the same path you took toward the cannery in chapter 2. At some green gloom you'll split up. You don't have the green crystal so you can't enter the green gloom. Instead head through the geometric door to your right. It's using one of the geometric keys you put together in a previous chapter.
Along the path you're on you'll come to a fork. Head left toward a cabin and you'll encounter some cultists to either dispatch or dodge. In the back of the cabin there's a hole you can crawl through to get in. Hopping out the window of the cabin will put you in a separate area from the cultists. From the window head right and you'll have large and small Cankertoads, 10:20 of the part 5 video. Defeat them and you can get what they're guarding, a piece to a new geometric key.
Now head back to the fork in the path and take the route to the right. In a clearing ahead surrounded by trees you'll see a path to the right. If you go down this path you can pick up mugwort, but you'll get attacked by a cultist. Not sure if you can avoid this attack by not going for the mugwort, but if you don't need it you may want to avoid this. If you still get attacked you can head back and grab it if you want. Further ahead is a 4 way intersection. The path forward is to the left. Straight ahead is a dead end with some resources and no enemies. To the right is a path leading up with some cultists at a ritual site. All that's up there is prismic crystals and ginger. No need to deal with these cultists if you don't want to.
Passing under the log on the path forward you'll come to another intersection. Head left for some unguarded resources. To the right you can find a spirit cap, a lore pickup, and the next geometric key piece inside a tent. I missed this on my initial pass through and had to come back for it while being pursued later. This is at 18 minutes into the part 5 video and 28:15 when I come back and find it.
Back at the intersection you now have to head into the gloom. You can fight the creatures or run and dodge through. Out the other side of the gloom you find your geometric door, but you're still missing 1 piece. Continue forward into the next gloom area and head to your right. There's a cabin here with your final geometric key piece, 20:15 of the part 5 video. If you continue past the cabin you'll find an optional Mandacore plant. Kill it to dispel the gloom if you want to, but not necessary to progress the story.
Once you start heading back for the geometric door you'll be attacked again by the fly entity. Heading to the door next to the cabin will loop you back around to the cabin at the fork we first encountered. Past this door to the right you'll find a path that drops you down near where you went under the log. You can either fight the flies to open the door before they re-form, or run down one of these paths to get some distance and loop back to the door before the entity catches up. Once through the door the entity stops pursuing you.
Follow the path to get near the lighthouse and re-establish communication with Maya. You'll pass through a geometric door that's already open. If you're exploring before re-uniting with Maya you might head left right after this and find a small shed with the door barricaded. Inside is a cultist. If you're trying to do a no cultist-kill run you might want to leave this door alone. All that's in there is a lore pickup and prismic crystals.
Explore the light house and get a cutscene with Maya at the top. Grab the key off the wall before heading back down. After exploring the lighthouse you're off to search the area for mercury to be able to turn the beacon at the top of the lighthouse. There aren't any enemies in the area right now so you can explore with pretty much no risk. The key you picked up goes to the cabin straight ahead of the lighthouse. The mercury solution is inside. Grab it, head back up the lighthouse, put the solution in at the first landing in the lighthouse and operate the pump, then head back to the top to point the beacon at the large prism.
At this point I think it's a bit too complicated to type up everything that comes next. In short the goal is to adjust the prisms on the ground to redirect the beam. From the large prism it splits into 2. I don't think it matters which one you follow first. Just follow one of the beams and as you come across prisms adjust them so they're aiming at the next until you're done, then repeat this for the other beam. If you're struggling with this you can follow along with the part 6 video starting at 4:45. When you finish both beams you'll be at the boss fight for this chapter.
The boss fight for this area is a 3-part fight. Damage the boss enough and it'll retreat. When it does run up the left or right side of the area to the crystals with the green beams and take out all of the spores flying down from the lighthouse. When done you'll have to leave the area with the crystal to fight in the central area again. Part 2 is the same as part 1, just use the crystal on the opposite side. Part 3 is a final fight against the boss. Deal enough damage and it's over. After the boss fight all that's left to this chapter is returning to Hannah.
If you found the video helpful, please consider giving a like and/or subscribe. This is a new channel on YouTube and any support is greatly appreciated
