Book Wyrm

Book Wyrms are neutral creatures added by Defiled Lands. They spawn inside defiled biomes where they replace passive animals, such as Pigs. Adult Book Wyrms will retaliate whenever them or any other nearby Book Wyrm is attacked, causing damage per attack, while babies will run away.

When killed, they drop 0-2 Raw Book Wyrm and 0-2 Book Wyrm Scale. If they were on fire, then the Raw Book Wyrm will be cooked.

Enchanted Book recycling
Book Wyrms can be fed Enchanted Books, which they will slowly digest for their "level value". This value is equal to the minimum amount of levels you have to spend to get this specific enchantment in an Enchanting Table, summed for each enchantment on the Enchanted Book. These can range from 1 (Efficiency I, Power I and Protection I among others) to 45 (Sharpness V) without any other mod adding enchantments.

Once a Book Wyrm has digested enough "level value", it will consume it to create a brand new Enchanted Book. This new Book can only have a single enchantment, unlike books enchanted at an Enchanting Table or found in dungeons.

Breeding
Book Wyrms can be bred using Foul Candy, similarly to vanilla animals such as Cows. However, unlike vanilla animals, Book Wyrms have several characteristics that can be passed and improved from generation to generation, contributing to making their Enchanted Book recycling better.

You can get the characteristics of a given Book Wyrm by using a Book Wyrm Analyzer on it.

Digesting time
This is the time, in game ticks, that the Book Wyrm will take to digest 1 "level value". It can range between 160 (8 seconds) and 240 (12 seconds) for wild ones, but can be improved through breeding all the way down to 1. For example, a Book Wyrm with a Digesting time of 200 (10 seconds) will take 3000 ticks (150 seconds) to fully digest a Fortune I Enchanted Book (worth 15 "level value").

Enchating Level
This is the amount of "level value" the Book Wyrm needs to digest before making a new Enchanted Book, as well as with how many levels will it enchant it. This ranges between 3 and 6 for wild ones, but can be improved up to 30 through breeding.

Golden
Wild Book Wyrms have a 1% chance of having a golden hide. Such Book Wyrms will drop Golden Book Wyrm Scales instead of the normal ones, and also have the ability to enchant recycled Enchanted Books with treasure enchantments (enchantments cannot be obtained through an Enchanting Table), such as Mending.

Breeding 2 non-golden Book Wyrms together has a 1% chance of giving a golden offspring, just like wild ones. This can be improved to 4% by having one of the parents be golden, and up to 10% by having both parents golden.

Trivia

 * The name "Book Wyrm" is a portmanteau for "bookworm" (an insect that eats through books ) and "wyrm" (a kind of mythological sea serpent ).
 * The name also comes from a card of the same name from the video game Hearthstone.