On top of the ramp you can find 1x Achilles Core Fragment C. Once you defeat them go up through the ramp located on the right part. Head down and defeat 1x Bayonet-wielding Knight Lost, 1x Elite Knight Lost, 3x Female Spiked Lost and 1x Horned Lost. Go up the ramp behind you to pick up 1x Old-World Materials.
You'll have to fight 1x Female Spiked Lost. If you interact with it, you can access the Horror Hunting Trials or increase the current difficulty. Keep going until you reach an open area where the Mistle is located.
Continue ahead and purify the Rotten Mistle.
Pick up 2x Regen Inducer, 2x Pure Blood, 1x Plasma Cartridge and 1x Fireproof Tonic. As soon as you enter the map you will see a table to your right.