Witch Water

Witch Water is a fluid added by Ex Nihilo which can be used to transform items and mobs.

Obtaining
To create Witch Water, right-click a Water-filled Barrel with Mushroom Stew or Ancient Spores. A Water-filled Barrel will also turn into Witch Water if placed near Mycelium. The time it takes to transform is based on the amount of nearby Mycelium blocks.

Barrel
While in a Barrel, Witch Water can be combined with certain other items to transform them.

Fluid
Witch Water can be removed from a Barrel with a Bucket (or fluid transporters such as Fluiducts). When placed in the world, Witch Water flows up to 7 blocks (like Water). Some mobs who come into contact with Witch Water are transformed:

Players (and friendly mobs not transformed by Witch Water) in contact with Witch Water are subjected to Blindness, Slowness, Weakness III, and Wither effects, and the effects persist for 10 seconds after losing contact.