Witches of Hemwick

The Witches of Hemwick are optional bosses in Bloodborne. They a pair of wicked witches who are able to use Arcane magic through rituals using the eyes of their victims. They resemble Eye Collector enemies with the exception of the abundance of eyes on their rags.

Lore
The witches are elderly hags who make a living by gouging out eyes of the folk in the Hemwick district of Yharnam. They use the eyes they collected to conduct rituals, granting them Arcane magic. During the nights, they summon paranormal monsters called Mad Ones to gather the eyes of the dead and living for the witches to obtain.

Hemwick Channel Lane
Upon entering the room, only the first witch's health bar is shown. She can summon Mad Ones into the room to pursue the player, able to summon up to three. The witch herself is invisible, but reveals herself when the player approaches at a melee distance. Once exposed, she will either attack with magic or teleport away to another part of the room. The second witch can appear, although her health bar does not show up until the first witch is defeated.

Once the first witch goes down, the second witch will summon three more Mad Ones, able to revive the first witch to half of her health should enough time pass. The witches are more aggressive during the second phase, as they can shoot out magic which temporarily immobilizes the Hunter, allowing Mad Ones to catch up and attack, or if one of the witches is nearby, she can grab the Hunter in attempt to gouge out their eyes, dealing massive damage. Defeating both witches cause all Mad Ones in the area to disappear into the ground.

Rotted Chalice Dungeons
If the Rotted Additional Rite is active, a witch can spawn in a random Rotted Chalice Dungeon. The difference compared to the witches in the Hemwick Channel Lane is their ability to summon Mad Ones more frequently, with a Mad One spawning almost immediately after one is defeated. But with their inability to go invisible, it is easier to located the witch when she teleports away. When defeated, the Mad Ones they summon will not disappear until they are defeated individually.

Trivia

 * If the Hunter has no Insight when fighting the Witches of Hemwick, they will be unable to summon any Mad Ones, making the fight ridiculously easy. But because the Hunter obtains Insight when they encounter the witches for the first time, they will be forced to let themselves die or use a Hunter's Mark to escape to the Hunter's Dream for them to use up their Insight before coming back.
 * In the Chalice Dungeons, the witches will always be able to summon Mad Ones even if the Hunter has no Insight with them.
 * Why the witches collect eyes in the first place is never answered, although there is conception this is their way to contact, or even ascend to, the Great Ones.