The Potion of Decay, also known as Potion of Wither or Potion of Festering Wither, is a potion of a black color, resembling that of a Wither Skeleton's skin tone. When inflicted upon an entity, it gives the Wither effect.
It is brewed from the Lava as the base fluid and Charred Bone as the ingredient. When combined with redstone, the Potion of Combustion can be elongated, doubling the duration of the Wither effect.
If the Potion of Decay is combined with glowstone, it will be amplified, doubling the damage of the Wither Effect.