This information is taken from the DBI notebook and has not recently been verified to be working. There are no credits on the document, so thank you to whoever.
Shadowbrook
Begin by going northwest from the room one south of the portal
continue going northwest and north until you hit a room with all 4 exits NSWE
go west from the crossroads until you can go Northwest or southwest, Go Northwest
go north until you hit a farm house, get the wax candle and the journal out of the table
go south and southeast, and then east until you get back to the NSWE room
go north, northeast, east, south
Get Matches box
Hold the matches to light the candle
go north west northwest east and north until you hit the oak tree room
The key should spawn in your inventory
Go back to the farmhouse, and east north of the entrance is a well
unlock down
go all down and east talk to the prophet
say Fate, and he'll give you two options, say "I will help you defeat Banos." (or similar) and he'll give you a keystone
go northeast north and you'll come to a split passageway east and west
go West, follow it around until you go to the rift
go south into the rift and you'll be teleported to a cave
go all the way north and down (be sure you have something with water breathing)
go all the way south, and southwest then northwest and up (“speedwalk nnddytsyru” from entrance)
you'll be in a room with a pedestel, Push arrow and walk southeast, northeast southeast southwest down south southwest east southeast southwest south south southeast (approximately) as fast as you can, the door south from there should be open (speedwalk dtqtydsyetsts)
go in and say Banos, he'll give you a talisman, and port you back to the entrance of the caves
Go back to the split passageway and go east this time
Follow it around and go into the rift
from here explore the area until you find the Chained demon towards the north of the area
Say "yes"
and say the option he gives you afterwards "I will collect ten spirits for you" or something similar (Punctuation is important)
He'll give you a soul snare
Go back up to shadowbrook and kill the vexed spirits for a chance to get the captured spirits ** NOTE:: They only spawn at night mud time
Once you've collected ten spirits bring them back to the chained demon and turn them in for the Shadow Dragon Fang
bring the fang to the shrine southwest a bit and east from the chained demon
drop the fang, and sacrifice it at Midnight Mud time to get the "Shadow Dragon Blade"
go west and northwest and southwest and wield the shadow dragon blade to kill the Hellbeast. You'll get the second banos fragment
go back to the split passage and you will auto-drop the 2 shards to get the fragment
Bring the fragment back to the prophet, and he'll give you the blue keystone
Go southeast south from the prophet to get to the southern Split passage
Take the east path and enter the rift, Go to the shrine in the center of the map, and put the candle inside, It'll teleport you inside
answer the riddles west, east, and south of the altar
The East riddle is "A candle"
the West riddle is "fireworks"
the south riddle is "Nothing"
go north to the altar, and you'll get a beryl stone
put the stone in the altar to be teleported down
go south, and say yes, Kill the knight and you'll get the first Castheon shard
take the West passage now and you'll be in a desert area
Go southeast till you can go east, then go northeast
you'll come to a sandstorm, Go north north to get to the Heart of the Sandstorm
from there go northwest, west, north, northwest then north
Tell the merchant You're here to go into the pyramid
He'll ask you for 10 million zeni, say you don't have that much zeni and he'll give you a key
go back into the sandstorm, and go east until you get back to the heart of the sandstorm, go south, and southwest to get out
go back out to shadowbrook, and go north of the oak tree in the cemetery..
Unlock the door, and go north, Kill the monster inside to get the Fragment of Sacred Edge
Repeat steps 44-47
The merchant will take the shard, and give you the pyramid key
Repeat step 50
go southeast until you hit the pyramid
Unlock the door, and put the pyramid key in your bag
go southeast, and the pyramid key will attempt to drop, but won't because it's in your bag
go south, east, and northwest until you hit the casket
say yes, and you'll get the other castheon shard
go back to the split passage, and both castheon shards will drop, and you'll get the fragment
go back to the prophet, and he'll give you the great keystone
go to the opposite side of the prophet, southeast and northwest, and west
go west twice, and kill banos, castheon, and banocastheon to get the head of banocastheon
Turn in the head to the prophet to to get either The devil's mark (power), The Devil's wings( don't remember) and The devil's halo (also don't remember)