Witch

A Witch is a ranged mob. It is the second hostile ranged mob to spawn in the Overworld - the first being the skeleton.

Appearance
Witches have a similar appearance to the villager mob, and they wear purple and green robes with brown leggings underneath. They have large noses (which moves slowly around on the Witch's face, as stated in Dinnerbone's tweet) with a single wart and have lavender colored eyes. They wear a stereotypical witch hat with a green buckle on it, and their skin is slightly paler than the normal villager. However, witches periodically give off purple star particles similar to the villager's green stars.

Combat
The witch mob uses splash potions, of poison, weakness, damage, and slowness, to fight the player. These potions will affect other mobs - not just the player. It does not burn in sunlight and when set on fire, drinks a potion of fire resistance. This can be seen when a bottle appears in the witch's hands. Iron Golems will attack witches as most other hostile mobs. Upon death, witches rarely drop potions of healing, swiftness, and fire resistance. Witches are immune to splash potions of poison, slowness, and instant damage. When damaged, they will drink potion of regeneration, healing themselves. When drinking a potion, a witch's nose will point straight forward (instead of down). While healing they can't attack the player. If lit on fire by lava or fire, witches will quickly drink potions of fire resistance, making lava and fire ineffective ways of killing witches.

A bow will likely be the best weapon for dealing with a Witch, as the splash potions have only a short range compared to them.

Trivia

 * If a witch shoots another witch with a potion, the witch who is hit will become angry but will not kill the other witch; instead, it will hit the offending witch once with a potion.
 * Though it's not actually a villager, the witch's skin is found in the Villager folder in the minecraft.jar.
 * Witches have more mob drops than any other mob.
 * Witches have the most health of any normally aggressive mob other than Boss mobs and Giants. However, maximum-sized Magma cubes may take more hits to kill due to their high armor value, and may also spawn numerous smaller versions whose collective health combined with that of their full-sized progenitor is well over that of one witch.
 * Witches are the first non-boss mob to naturally regenerate health.