"And so my face shall become that of death, and of life perverted." -Mordvig Nightberry.
The Skull of the Root is a mask formerly worn by Mordvig Nightberry. It is in the possession of Jack.
The Skull is a mask made from thick roots. While it possible to see through the eye holes, from the outside, the eye holes appear as black voids. The roots wrap around the wearers head when put on, releasing when taken off.
The Skull was created by Mordvig Nightberry during The Age of Winter, shortly after the death of Kochanka Nightberry. It was worn by him for the next 300 years, until his death at the hands of The Children of Frost, after which it was acquired by Jack.
While wearing the Skull, you can use any creature under your magical influence (e.g. charmed by you, a construct of yours, a familiar of yours, under the effects of suggestion or similar, etc) as a conduit for any spell or magical effect you can use. The creature you use this way casts the spell or magical effect as though it had cast it, and acts in the required fashion to perform the spell. The spell or ability is still considered expended by you however. You can perform this on the creature's turn as well as yours if your Wisdom Score is 12 or higher, and if you are affecting multiple creatures this way, you can use this effect on a number of creature's turns equal to your Wisdom Modifier.