In Mortal Shell 2, the Slaughterer's Sigil is a highly useful special sigil. To obtain it, head to Marrowkeep. From the marked location, go left, and you'll find the Slaughterer's Sigil directly on a throne. This sigil has a significant effect, greatly reducing the game's difficulty, but it will not unlock achievements.
How to Obtain the Slaughterer's Sigil in Mortal Shell 2