D&D General What would your "fourth core rulebook" be?

[Scribe]

This fourth core book might be homebrew, official like Eberron or Forgotten Realms, or indy.

 

[sevenbastard]

The Homebrew Handbook
Or the
The Tinkers Toolkit

A rules builders tool box. The PHB gives you classes and species, the DMG magic items and how to run the game, the MM foes, but what would be great is a book about designing your own game.

Basically make D&D yours. Here is 100 pages of house rules what they accomplish how they change the game and how they interact with other rules. 50 pages on building classes, 50 pages on building monsters, ect.

For example 15 diffrent rules variations on what happens at zero HP. 10 diffrent ways to use death saving throws, 12 diffent ways to change how HP are regained, ect.

Pros and cons, how to ballance, how to playtest, what to avoid, ect.

Then when I start a game it's 5e, but I'm using the Cleric variant no cantrips extra spell slots, exhaustion on a failed death save, no dark vision, and xp for gold.

 

[I'm A Banana]

A book on how to create new things for the game that serves as a kind of "director's commentary." I want monster building, class building, subclass building, I want a design advice and dpr charts, I want the game-makers to show me how to bend this system over my knee and make it what I want.

I do realize that this document would probably inspire a million and one internet arguments, but I'd find it very useful personally.

 

[Shiroiken]

I've always considered the campaign setting book to be the "fourth core" book for any given campaign. However, with the modular nature of 5E, I could see a book designed to tweak different options to generate specific themes. Honor and Horror rules, for example, would be found there, instead of in the DMG.

My first thought is whatever setting they want as a sample and default. So Greyhawk, Forgotten Realms, Nentir Vale.

A sample and a baseline. So the monster manual lore would tie into a vision that fits that baseline and not be vague generic. Other worlds like Eberron (dinosaur riding halflings) and Dark Sun (cannibal halflings) can vary from that default lore significantly, but the core can have specifics as a default and not just be an SRD of stats to create your own stuff around.

This has actually been a problem for D&D for a while. Almost every other RPG is designed to be used in a specific setting, rather than a generic one. Having a "default" setting book that uses the lore from the other three core rules would be ideal. Other setting would then have descriptions of how their setting differs from the default. As much as I dislike 4E, the decision to use Nentir Vale as their default setting was a good one.

 

[Umbran]

What about you?

Mordenkainen's Manual of Styles. How to run a sandbox. How to run story-forward. How to run gritty. How to run hexcrawl. How to run dungeon crawl. How to run low magic. How to run epic fantasy. How to run low fantasy. How to run low-combat. How to run high/low lethality. How to run a mystery....

A book that gives rules tweaks and design changes to support a variety styles of play.

 

[CherubKid]

Along the way, various tomes have vied for the spot as the "fourth core"; growing up in the 80s, I always felt like Deities & Demigods best fit that place, at least in terms of prominence within my young D&D-inspired imagination. But Unearthed Arcana, various iterations of a "PHB 2" or a Fiend Folio or MM2, an epic level book, not to mention setting bibles, have had their place.

Seconded! The first edition Deities & Demigods has a special place in my heart and has always been part of my "Core Four" Advanced Dungeons & Dragons tomes, melding my obsession with the game and my love for mythology. (Awesome avatar, by the way!)

And further, it opened up the game (for me, at least) in so many new directions... expanding ability scores beyond 18 (or beyond 18(00) for those who appreciate such obscurities), appendices expanding the scope and lore of the inner and outer planes, establishing gods for elves, goblins, dwarves, orcs and over a dozen more "nonhuman" humanoids.

(and then... sorta ninja'd by Umbran )
Having said that, what would feel most "Fourthcore" (not a word) to me would be an Explorer's Tome (still workshopping the name)...

A book with guidelines and tailored sub-systems for two or three dozen fantasy genres... with maybe one or two new classes (or subclasses) and/or PC species for each. The new DM's Guide touches on this in the Creating Campaigns chapter and then gives us the Greyhawk setting for 24+ pages. But instead of pre-named, copywritten worlds, give me a variety of iconic genre settings, each with its own distinct flavor.

So you could have (among others) a steampunk chapter, Arthurian, fairy tale, a Greco-Roman setting, a high seas or swashbuckling setting, gothic horror and so forth; maybe a renaissance and a medieval couple of chapters, maybe a wasteland setting, a Western/fantasy mashup, and something akin to the Underdark? Maybe guidelines for magical school settings (I know Strixhaven is a thing), or even a generic world of competitive roaming monster-collectors.

Campaign setting books have their place, but I'd cherish a book of iconic campaign settings.

 

[DeviousQuail]

The "Basic & Advanced Rules" is a great suggestion. A place to stick rules like spell/martial combos, rituals and spells that are meant for NPCs, wealth tables, playing with no or more complex skills, and any other modular stuff. I'd probably even include the other genres variations with class, subclass, and item differences. A book dedicated to getting the most out of the other 3.

 

[dave2008]

A alternate and optional rules book. Guidelines and mechanics for playing in different genres and styles. And for 5e24 - monster creation rules!

 

[Chaltab]

Echoing what others have said, but a DM's Toolkit that includes things to adjust play beyond the basic parameters. Maybe include that tactical module they promised us during the D&D Next playtest and then never delivered on, as well as dials and advice for running story based campaigns, sandbox campaigns, West Marches, mysteries, Epic Level Play.

 

[Bomberooski]

I’d be cool with a “Elfsong Tavern’s Tables, Treasures and Tips”

Random tables for PC’s and DM’s. A whole slew of magical items and weapons. And a bunch of tips that could include alternate ways to approach rules depending on who is at your table.