The witch hat is a helmet item that gives +3 armor and has 200 durability. It’s traded by the wandering witch and dropped by witches about 7.5% of the time. (100% when the witch is killed by a charged creeper.) It accepts helmet enchantments.
It increases drop chances and amounts of potion ingredients for the following mobs:
Rabbit: Drops rabbit’s foot 100% of the time
Glow Lichen Zombie: drops sightless eye 100% of the time
Ghast: Drops 2 more ghast tears & 2 more gunpowder
Phantom: Drops 2 more phantom membrane
Magma Cube: Drops 2 more magma cream
Breeze: Drops 2 more breeze rods
Spiders: Drop 2 more spider eyes
Witch: Drops 2 more of their random potion ingredient drop
Creeper: Drops 2 more gunpowder
Geomancer: drops 2 more amethyst dust

Quite a fashion statement! It can also be dyed if you want to make sure it matches your outfit.
History
| 1.5.5 | * | Witches and ender dragons will now only drop one instance of their hat/head when killed by a charged creeper, similarly to other mobs that drop heads. | |
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| 1.5.0 | * |
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| 1.4.0 | * | Breezes now drop more breeze rods when killed by players wearing witch hats | |
| 1.3.2 | * | The witch hat has been completely reworked to have a new purpose (that isn’t just a cool hat!) When killing mobs that drop potion ingredients, they will now have higher drop rates of these ingredients. This includes:
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| 1.1.0 | Beta 4 | * | Witch hats now give the same amount of armor as diamond armor, but with only 100 durability. (This is to make up for the removal of their other usage, witch trading (see below)) |
| 1.0.0 | + | Witches killed by charged creepers will always drop a witch hat | |