From recall proceed to the down, pit beast area is one further down.
Paralyzes, keep webbed to prevent bashing. You'll need to cut off all its tentacles before being able to really dmg it hence the combat aim arms. After you stop seeing tentacles being slashed off, you can switch back to combat aim <your preference>. It'll start emoting damage on the tank. Keep tank healed and it'll go down. When it's low it will start fleeing.
a broken cameo
a fuzzy green key
a fine chisel which accesses armored dragon
a brass tetrahedron which part of Mark of Legacies