Isaac Quest Guide: Lords Of The Fallen

Begin by looting the Flayed Skin from the Abandoned Redcopse.

Visit the Umbral Scouring in Calrath City. This memory is found on the right side of the burning pathway as you enter the city from Fitzroy's Gorge.

Proceed to the Fief of Winter’s Curse. After defeating the Fire Giant boss in Calrath City, return to the hub and find a note. Use the Fief key to open a door near the windmill vestige in Abandoned Redcopse. Navigate the cave system, defeat the Kinragr Guardian mini-boss, and find an Umbral Scouring memory in front of the Fief Vestige.

To find the next Umbral Scouring in the Fief, you must lift the gate at the fief vestige. Climb the ruin ladder, go left of the gate to a cliffside pathway, follow it down, and go over a bridge. Return towards the ruin, use an umbral platform to reach the ruined roof, and pull the lever. Follow the new pathway down through a cave and a ruined castle, explore the sunken village, and enter the raised castle rampart area to defeat the beacon boss. After defeating the beacon boss, descend a tower into a larger arena to fight the Lightreaper. An Umbral Scouring memory is located just outside this arena.

Travel to the Path of Devotion, located to the right of the Bell-Rise boss. Work your way down to the Sin Piercer Archer. Enter Umbral and create a path to a floating arena island to fight Paladin Isaac's Umbral form. Claim the Umbral-Tinged Flayed Skin after defeating him.

Return to Abandoned Redcopse and go to the location where you found the initial Flayed Skin. Use the Umbral-Tinged Flayed Skin to open the blocked door.

Defeat the Lightreaper. You can summon Isaac as a phantom after dying to him once.