After passing through the corridor, you will reach a set of stairs where a group of Noctilucale wait at the bottom. These are similar to Frag Leeches and are vulnerable to both Fire and Ice. Thankfully, they are easily dispatched if you use area of effect attacks to whittle down their numbers.
In the central area are a trio of neon green Phosphoric Ooze who, like other flans, are weak to elemental attacks - in this case Fire. They can also combine to create a stronger version of themselves; the Alchemic Ooze. After killing them, run back (away from the marker) to reach another group of enemies guarding yet another treasure, inside which is a Saint’s Amulet .
Follow the marker on, killing a giant group of Noctilucale and a mixed concoction of Phosphoric Ooze and Noctilucale along the way. At the end the path splits in two and you should choose the right-hand path first. Jump up the debris and follow the track to a dead end, complete with a mass of Noctilucale and a Treasure Sphere which contains 10x Medicinal Oil .
Return to the split and take the left path this time. Four Phosphoric Ooze will spring up from the ground as you reach the next track so take care of them and head forward, jumping over more debris. When you reach the split near the Save Station, turn around to the dead end at the back and collect the Rainbow Anklet then turn around and head to the Save Station.