The Kanohi Farax is the Mask of Pain. It has the power to create pain in any being, but it cannot remove it nor can it cause death (Although the pain usually makes the target wish for death.)
In the epic universes by Mtmerrick, Masks of Pain are common Kanohi for Toa of Shadow. Radiak wears a matoran version of the Mask of Pain. This mask also serves as the symbol of the Toa of Shadow.