Thorns

The Thorns enchantment was primarily used on Chest Plates but can be used for Helmets, Leggings, Boots, and even the turtle shell. When the wearer is attacked, the enchantment will inflict damage on the attacker. This enchantment is similar to how Guardians and Elder Guardians will damage players when their spikes are out. However, this enchantment will work when damaged by any form including ranged attacks.

A skeleton taking damage after shooting a player with arrows (via screenshot)

What is the use of Thorns?

When wearing any piece of armor with the Thorns Enchantment, the wearer will have a chance of inflicting damage between 1-4 to their attackers. The chance and the amount of damage increases as the level of the enchantment increases. Regardless of whether it was a melee hit or even a ranged attack, the attacker can receive damage and knockback from the enchantment. With multiple armor pieces, the enchantment will stack but the total amount of damage that can be dealt is capped at 4. The following table will show the probability of the maximum and average damage that is dealt with multiple items with the Thorn Enchantment:

Items with Thorn III	Probability of max. damage 4	Average damage dealt
1	11.25%	1.125
2	28.83%	1.997
3	46.33%	2.637
4	61.18%	3.09

How to obtain Thorns?

Like most other enchantments Thorns I & II can be obtained from regular methods such as fishing, trading with villagers, enchantment tables, or loot from chests in generated structures. But to obtain Thorn III, you will need to combine two Thorn II enchanted books. The only other way to find an enchanted book with Thorn III is through loot chests in generated structures.

Combining two thorn II enchanted books to get a thorn III enchanted book (via screenshot)

Conclusion

Thorns can be a useful enchantment if you like to pick fights with a ton of mobs or just like to play aggressively. Getting the highest level of Thorns is highly recommended even though it is quite troublesome to do so.