Welcome back, adventurer! Ready to explore the depths of history and the dungeon where it all began?

By 1975, Dungeons & Dragons was evolving at an unprecedented pace. With the release of Greyhawk, the first supplement, the game had taken significant strides in refining mechanics and adding depth. But the second official expansion, Dungeons & Dragons: Supplement II: Blackmoor, introduced something even more exciting: underwater adventures, assassins, and the concept of dungeon ecology (or, at least, an attempt at it).

Created by Dave Arneson, Blackmoor was a direct extension of his personal campaign world, the first-ever fully fleshed-out setting in D&D history. But was it a game-changer, or just a bizarre collection of ideas? Let’s dive deep into Blackmoor (both literally and figuratively) to uncover its impact, quirks, and long-lasting influence.

What Was Blackmoor, Anyway?

Before Blackmoor was a supplement, it was the campaign that started it all. Dave Arneson, co-creator of Dungeons & Dragons, had been running an elaborate, evolving game world called Blackmoor for his players long before the official rules of D&D even existed. His campaigns emphasized exploration, player freedom, and a bit more chaos than the Greyhawk campaign by Gary Gygax.

When TSR published Blackmoor as a supplement, it carried over Arneson’s distinctive style: a blend of traditional medieval fantasy, weird technology, and deeply dangerous dungeons. While Greyhawk laid the foundation for mechanical improvements, Blackmoor focused on world-building, unique gameplay experiences, and some truly strange additions.

What Did Blackmoor Add to D&D?

Like Greyhawk, Blackmoor expanded the original Dungeons & Dragons ruleset. But where Greyhawk focused on refining mechanics, Blackmoor introduced new classes, monsters, and even a legendary adventure module that set the stage for future campaigns.

1. The Assassin – Because Every Party Needed More Trust Issues

Let’s start with the most infamous addition: the Assassin class. Unlike Fighters, Clerics, and Wizards who (mostly) worked for the good of the party, Assassins had a very specific role: killing people, preferably for money.

• Assassins could disguise themselves, use poison, and execute enemies with instant-death strikes.
• They had their own Assassins’ Guild, which meant your character was part of an underground network of deadly killers.
• And, most controversially, they could only reach higher levels by assassinating other, higher-ranked assassins—even potential party members!

Nothing says teamwork like knowing your sneaky “friend” is waiting for the right moment to level up by murdering you in your sleep.

2. The Monk – Because Martial Arts and Medieval Fantasy Go Great Together

The Blackmoor supplement also introduced the Monk, an unarmed warrior with a heavy Eastern influence. Inspired by Shaolin martial artists, Monks brought kung-fu fighting into D&D, proving that a character didn’t need weapons to be deadly.

• Monks had a unique attack progression, dealing more damage with their fists as they leveled up.
• They were fast, hard to hit, and could dodge attacks with their uncanny reflexes.
• They had an odd mix of magical and physical abilities, including resistance to mind control and the ability to survive falls that would splatter any normal adventurer.

Though Monks have gone through many iterations in later editions, Blackmoor was where they made their grand entrance, adding an exciting new flavor to character choices.

3. The First Aquatic Adventures – Time to Get Your Feet Wet

Ever wondered why D&D had so many underwater creatures but no real rules for handling the ocean depths? Well, before Blackmoor, there weren’t really any. This supplement introduced underwater combat mechanics, rules for movement, and new monsters like the Sahuagin—the shark-like creatures who have been tormenting adventurers ever since.

These rules set the stage for future underwater campaigns, though early DMs quickly realized that drowning was a very real threat when players inevitably forgot to prepare for subaquatic survival.

4. The Temple of the Frog – D&D’s First Published Adventure Module

One of Blackmoor’s biggest contributions was The Temple of the Frog, often considered the first-ever published D&D adventure module.

• Set in a sinister swamp temple, this module featured a cult of mutant frog-men who had some shockingly advanced technology.
• The villain, Stephen the Rock, wielded sci-fi-style high-tech weaponry, proving that Arneson really liked mixing fantasy and science fiction.
• It was massive, with over 100 rooms, complex enemy factions, and an emphasis on infiltration and strategy rather than just brute force.

Many modern dungeon modules owe their complex layouts and faction-based storytelling to The Temple of the Frog. It wasn’t just about hacking through corridors—it was a living world that could react to players’ choices.

How Blackmoor Changed D&D Forever

While Blackmoor wasn’t as mechanically groundbreaking as Greyhawk, it pushed the boundaries of what a D&D setting could be.

• It introduced detailed world-building elements that encouraged DMs to create dynamic, reactive game worlds.
• It added new classes that expanded character variety, even if some (looking at you, Assassins) caused party tension.
• It laid the groundwork for adventure modules, proving that a structured, story-driven experience could be just as engaging as open ended dungeon crawls.
• It was one of the first expansions to blend fantasy with science fiction, something D&D would explore further in settings like Expedition to the Barrier Peaks.

Even if many of its mechanics were later refined (or abandoned entirely), Blackmoor was an essential step in D&D’s evolution. It demonstrated that D&D could be more than just hacking monsters in a dungeon—it could be about intrigue, exploration, and even underwater survival.

Final Thoughts: A Strange but Essential Piece of D&D History

Looking back, Blackmoor is a fascinating mix of brilliant ideas, weird experiments, and some truly questionable mechanics (seriously, an entire class based on murdering other characters?). Yet, it remains one of the most influential supplements in D&D history.

So, the next time your party fights an Assassin, recruits a Monk, or nearly drowns because no one prepared Water Breathing, remember: it all started with Blackmoor.

Now, go forth, adventurers! And maybe pack a snorkel—just in case.