The Compendium Aegis
No one knows who assembled the first entry in the Compendium Aegis, the oldest inscription is written in a script that linguists date to an age before the current calendar and describes a creature that no surviving bestiary has ever recorded. The shield has passed through at least forty documented keepers across three planes, each one a seeker of hidden things: archivists, explorers, obsessive historians, and more than a few who simply could not stop asking questions until the questions consumed them. It does not choose its wielders so much as find them, it has a habit of turning up in curio shops, estate auctions, and the back shelves of libraries, always priced too low, always already half-familiar to the person who picks it up.
Mechanics
A living archive bound into a shield, the Compendium Aegis grows more powerful as its wielder uncovers the secrets of the creatures and planes it has catalogued across centuries.
The Catalogue, Living Record
The shield's inner face is covered in dense, shifting script, entries written in dozens of hands across hundreds of years. Whenever the attuned wielder kills a creature of CR 1 or higher, or succeeds on a DC 15 Intelligence (Arcana, History, or Nature) check to recall lore about a creature type, plane, or forgotten location during a short or long rest, one new entry is inscribed onto the shield in pale silver ink. The shield can hold a maximum of 100 entries. Entries never fade and survive the death of the attuned wielder, the shield remembers everything.
Residual Ward
For each entry recorded in the Catalogue, the shield hums faintly with accumulated memory. The shield grants a +2 bonus to AC (in addition to its normal shield bonus) as long as it holds 25 or more entries, and a +3 bonus to AC as long as it holds 60 or more entries. These bonuses are always active and stack with the shield's base +2 AC.
Planar Attunement
The Compendium Aegis carries impressions of every plane its previous keepers passed through. You have advantage on Intelligence checks made to recall information about any plane of existence. Additionally, when you enter a plane for the first time, you may ask the DM one question about that plane, its dangers, its dominant factions, or the nature of its magic, and receive a truthful, useful answer drawn from the shield's historical record.
Resonant Knowledge
When a creature you can see makes an attack against you, you may use your reaction to consult the Catalogue. If the shield contains an entry for that creature's type (beast, fiend, aberration, etc.), you impose disadvantage on that attack roll as the shield's wards align precisely against the threat it has studied. You may use this reaction a number of times equal to your Intelligence modifier (minimum 1) per long rest.
Unwritten Page
Once per dawn, you may press the shield against an object, a sealed door, a ruin wall, or a creature that is incapacitated or willing, and speak the command phrase inscribed on the shield's boss: a single word in a dead language that each new wielder somehow reads as their own name. The shield makes an Arcane History check (treat as 1d20 + 11). On a 15 or higher, the shield reveals a hidden truth about the object, location, or creature, a secret room, a creature's true name, the purpose of a forgotten mechanism, the origin of a curse, or a fragment of lost lore, as determined by the DM. This ability does not create information that does not exist in the world; it uncovers what was already there, buried. On a failure, the shield's script roils for a moment and goes still, and that object or creature cannot be targeted by this ability again until the next dawn.
The Final Folio
When the Catalogue reaches 100 entries, the shield undergoes a visible transformation: the silver ink turns gold, and a single blank page, the only blank space anywhere on the shield, appears at its center. This page cannot be written on by any means except one: the death of the attuned wielder while holding the shield. If the attuned wielder dies while holding the shield with 100 entries, the Final Folio records a complete account of that wielder's life, memories, and knowledge, compressed into a single page. A new attuned wielder who reads this page over the course of 10 minutes gains the benefits of the Legend Lore spell about any single subject the previous wielder knew intimately, their greatest discovery, their deepest secret, or the mystery they died pursuing. The page then fills, and the Catalogue resets to 0 entries, beginning anew.
DM Notes
Balance consideration: The +3 AC bonus at 60 entries is the most significant numerical effect and effectively makes this shield equivalent to a +3 shield once fully developed, keep this in mind if the party already has high AC. The Catalogue entry system is the heart of the item and should be tracked carefully; consider keeping a shared document or index card. Resonant Knowledge is strong but depletes quickly, especially at lower Intelligence modifiers, it rewards Intelligence-primary builds without being overwhelming on other classes. The Unwritten Page is deliberately DM-facing: it should never produce information the DM hasn't already decided exists in the world, making it a tool for collaborative worldbuilding rather than a way to bypass puzzles. The Final Folio is a generational mechanic; it is most meaningful in long campaigns where the previous owner was a known figure. For a collector character, consider seeding early sessions with objects, ruins, or creatures that connect to existing Catalogue entries, the shield's lore invites threads that pull the party toward planar mysteries. Recommended pace for entries: roughly 2-5 per session in an active campaign, meaning the shield reaches full power after 20-50 sessions of play, making it a long-term investment rather than an immediate power spike.
Generated with: Level 17 · Artificer · Artillerist · Armor (Shield) · A theme that fits his character · Heroic · Legendary