The step-pyramid. It cannot move, capture or be captured, and other pieces of either colour are not obstructed by it and can even stand on top of the step-pyramid as if the square were empty. Each side has one step-pyramid at the start of the game in addition to their normal allowance, and secretly records which square it occupies. Note that it is legal for both step-pyramids to occupy the same square.
---And damn me if someone else hasn't had the same idea already, more or less. Gah.
The death reflect piece.
Each time you look at it you see the reflection of a loved one who died or someone in your family who has passed away screaming in fear and pain calling your name begging you, "Please make it stop!"