Fermented Spider Eye

The Fermented Spider Eye is a potion ingredient used to brew potions with negative effects. It can be crafted from a spider eye, brown mushroom, and sugar on a crafting grid. They are inedible, unlike the regular spider eye.

As drinking any potion with a negative effect yourself is quite a silly thing to do, the potions are often brewed into a splash potion with gunpowder, making them throwable weapons that inflict their effects on mobs/players instantly. However, throwing the potion too close causes the player to suffer from effects too.

Crafting
The items needed can be put in any shape.

As a Brewing ingredient
to make the potion of slowness you need fire potion + fermented spider eye

Trivia

 * Fermented spider eyes corrupt the effects of a potion they're used on.
 * Undead mobs, such as zombies, skeletons and zombie pigmen, are actually healed when hit by a potion with instant damage. Similarly, attacking them with a healing potion makes them take damage.