Differences Between OD&D and FMC

I thought it would be useful to have a list of differences between OD&D and my retroclone Fantastic Medieval Campaigns, at least as far as I can tell (and I could be an unreliable narrator!). I hope it’s clear from the list that I’ve mostly striven for user friendliness with regards to the text content as opposed to inserting myself as an editor of the ruleset as such – that’s what you have Holmes, Moldvay, Cook, and Mentzer for, and I’m pretty tired of systematic reiterations of this same ruleset.

The goal, to reiterate (lol), is to re-present the primordial soup of the little brown books in order to understand in what context were they written, for what they were intended, and why they were transformed over time by the aforementioned “editors” as well as by Gygax himself. We good?

Without further ado, here’s all the changes I can think of:

• Magical manufacture and research moved to the end of the first chapter, after spell descriptions, rather than being included as part of the mage's class description.
  
• Undead monsters consolidated on cosmic alignment table, in order to produce a list of 20 chaotic entries.
• Inline annotations for ascending armor class, explained explicitly in the optional rules appendix.
• Percentile rolls often replaced with twenty-sided dice rolls where applicable (i.e. where the original used intervals of 5%, equivalent to 1-in-20).
• Many references to x-in-6 have been replaced with fractions of ^x/₆ as a stylistic decision.
• Fighting-men renamed to “fighters”.
• Magic-users renamed to “mages”.
• “Village Priest” cleric title renamed to “Priest”.
• Experience level tables and combat statistics tables combined into one for each class.
• High-level class statistics (e.g. tenth-level fighters) presented in the table above rather than in a separate body paragraph about unlisted levels.
• Spell descriptions for each level are in alphabetical order, although the spell lists themselves are in the original order.
• Monster reference tables are categorized by monster type, and includes monsters previously represented as groups rather than as individuals (such as bandits etc. originally being listed on one row just as “Men”).
• Goblins and kobolds are presented on different rows rather than the same row of the monster reference table; same for skeletons and zombies.
• Balrogs have been renamed to balors.
• Monster descriptions presented in alphabetical order rather than in order of presentation on the reference tables.
• Sea monsters described in the section on monsters (in Chapter II) rather than in the section on oceanic combat (in Chapter III).
• References to “men” generally replaced with “humanfolk” when referring to fictional human beings, or to “figures” when referring to tabletop wargaming figures.
• Example dungeon is completely new.
• Peasants in the wargaming rules have been simplified rather than having different target scores to attack and defend against different kinds of figures. This might be the only actual rules change.
• Optional rules are included in an appendix.

The optional rules appendix is definitely more involved than the above, but it's set apart from the main body of the text such that there should be no confusion about them being non-original or apocryphal in nature.

Thanks to my friend Alex Chalk of To Distant Lands for asking about this! It seems important to set straight just to know, if anything was changed, what and why.