This is part of a first-playthrough guide using the Dragon story arc. It covers both the original PSX version and the 2021 HD remaster, though some place and item names differ slightly in the latter. You can find an overview of the Dragon% path here.
The Quick Version
After you’ve completed The Field Trip, return to the Bone Fortress and the folks in the village will be freaking out. Fight to enter the Cranium gate, then explore the fortress to find the second of the three dragons Larc is seeking. After a series of boss fights, you’ll get the Green Cane Artifact as your reward.
The Details (May Contain Spoilers)
The Bone Fortress can feel like a maze, but the layout is actually not too bad. Each of the four floors is fairly small and self-contained, and apart from the trap that you trigger at the beginning, the only way to get between floors is the elevator.
To get into the fortress from the Cranium Gate, you’ll have to fight the Skeletal Soldier. This fight is not a big deal compared to bosses and minibosses you’ve seen already in this quest line. Entering the fortress, you’ll see a set of three large switches that look like tables. Inspect them, and a trap will send you to the basement of the fortress.
In the Basement
Go to the bottom of the screen, then left to get to the Vertebrae Room. There, talk to a skull, then head left through the newly opened exit and talk to the suit of armor. This opens another door, this time to the right. Go through it and recover your pet.
Backtrack to the room you fell into before and inspect one of the switches to open the door to the elevator. Take the elevator to the third floor.
On the Third Floor
Ass soon as you get out of the elevator here, you’ll be pushed into a fight with miniboss Sierra. She drops the key that you need to recover Larc, your third party member. With key in hand, turn right around and take the elevator to the second floor.
On the Second Floor
Go to the left, then talk to the suit of armor to open a door. Go through it and collect Larc, then backtrack to the elevator and return to the third floor.
Back on the Third Floor
This part’s more or less a straight shot. Head left from the room where you fought Sierra, then up the stairs to the Ribcage Hallway to fight Deathbringer. From there, go right to the Throne of Corpses and fight Jajara. Defeating this double-dip boss brings you to the end of the quest.
I entered the Bone Fortress after completing The Field Trip, but nothing changed and the Cranium Gate still won’t open.
You need Larc in your party to advance with this quest. If you dropped him (e.g., to pick up another NPC) you can collect him from the entrance room of the Underworld map.
I got through the Cranium Gate but am “one person short” to press the switches.
Grab a pet from the Monster Corral. Pets are people for our purposes. 🙂
That Sierra fight is tough!
Despite being a miniboss, Sierra is arguably the most difficult battle in this quest, partly because you don’t have Larc in your party until after you defeat her. She has lots of HP relative to earlier minibosses and doesn’t give you nicely telegraphed attacks like a regular boss. The big danger with Sierra is letting her juggle you with her frontal double-dash attack, which can carve away at your HP quickly. Basically, any time you see her dashing forward and swiping from side to side with her daggers, you want to sidestep. She stands still, and is vulnerable, for a moment after.
Using your normal heavy attack (Square button) can be hazardous here because it leaves you a sitting duck. The default 1H Sword moveset includes an uppercut (Square, then Triangle in quick succession) that has little recovery time, moderate damage, and decent knockback. If you can time these when Sierra is jumping—which she does a lot—it’s less of an issue whether you can hit her on the ground, where she is much more dangerous.