This Artifact can be found in Chapter 28 - The Trial of Archimedes. After clearing all of the enemies in the trials, you will have to close the doors that are open and then pull the dark magic-covered switch all the way back. Activate your clone, then go through the portal. This will cause the entire platform to lower to the bottom. Run to the right side of the cage to find the Artifact on the ground.
When activated, this item will slowly cause your health to drain. Note that it will never kill you, though.
