What the four giant's codices do in High Five, the ordinary one, Mastery, Discipline and Oblivion, and where each of them is knocked out or spoiled from monsters.
Giant's Codex
Giant's Codex in the High Five chronicle is the same plain book Secret Book of Giants, only renamed in the chronicles above Interlude. Apart from the new name everything remains as usual: skills are enchanted with the books; with one book you can enchant a skill as far as it goes, but if a failure happens, the enchant drops to zero and the book disappears. The enchanting itself is described in the article Skill enchanting: requirements, routes and what happens on failure.
But there are some differences too, not in the mechanism of action but in that this book can now be obtained from mobs. There are plenty of mobs with the drop of the codex (sixty of them): the best drop is in the Dragon Valley, reworked in the High Five chronicle; very many mobs are in the School of Dark Arts location added in the Freya chronicle; practically all the mobs of the Field of Silence, reworked in Freya; several mobs in the Beast Farm, reworked in Freya; and a few more locations that were reworked and settled with new mobs. But there are only two mobs with the spoil, one in the new Dragon Valley and the other in the school, which is unpleasant too, since the location is packed with mobs to the brim; but all the same it is much easier here than among the dragons.
Giant's Codex - Mastery
Giant's Codex - Mastery: unlike the ordinary book, with it a skill can be enchanted so that on a failed enchant the skill is not reset but stays at the previous level. The Mastery book was added to the content after the Interlude chronicle, when the skill enchanting interface itself had changed and it was no longer necessary to run to the masters to enchant skills. The blessed enchanting also differs from the ordinary one in that it needs three times as much SP.
There are already far fewer mobs with the drop of the codex of mastery than with the drop of the ordinary codex, and these mobs are much stronger, and the locations where they are found are no longer for a stroll: these are the Seed of Annihilation and the Lair of Antharas reworked in High Five. And there is one exception, a mob from the Giant's Cave reworked in Freya. With spoil it is quite sad: only one mob, and you can go there only in a party.
Giant's Codex - Discipline
Giant's Codex - Discipline: with this book you can change the direction of a skill's enchant to another path; for example, you enchanted some dance for lower mana consumption up to +15, and then joined a clan where you were told that they do not care about mana and the skill has to be re-enchanted for a longer duration. That is when you will need this book, so as not to relearn everything from scratch but simply switch the direction of the enchant from mana to time. When the path is changed, the overall enchant level of the skill goes down by one to three points. The Discipline book was added after the Interlude chronicle; changing the direction costs a certain amount of SP and adena.
There are quite few mobs with the drop of the codex of discipline, and the locations are mostly different already: only the Lair of Antharas reworked in High Five and the Giant's Cave reworked in Freya remain, and new ones were added, mainly the reworked Mithril Mines. There is no spoil at all: this is the only codex of all that is not spoiled.
Giant's Codex - Oblivion
Giant's Codex - Oblivion: with this book you can cancel the enchant of a skill. But to be honest, I do not quite understand what this should be done for at all. Changing the direction of the enchant is clear, that may come in handy, but dropping the enchant to zero is beyond my understanding. All the more so as the enchant is not reset at once: a separate book is needed for lowering each enchant level of the skill. The Oblivion book was added after the Interlude chronicle; cancelling the enchant returns a certain amount of SP.
There are quite few mobs with the drop of the codex of oblivion, and the locations are mostly different already: only the Lair of Antharas reworked in High Five and the Giant's Cave reworked in Freya remain, and new ones were added, mainly the reworked Mithril Mines. The spoil is from only one mob in a top location, and there are extremely few of these mobs there, and their respawn is for some reason slowed down.
On the page of each codex there is the full list of the monsters it drops and is spoiled from, with chances.