I must create a system, or be enslaved by another man's. I will not reason and compare: my business is to create.

- William Blake

Tuesday, February 03, 2026

Prismatic Planet - Introduction

About RPGs and How to Play Them

If you're reading this, it's likely you've played RPGs before. If not, there are plenty of good, free ways to learn. You can read my short tutorial, learn from someone who already plays, watch online videos, and so on.

This game assumes you're already familiar with RPGs—especially the world's most famous one—and particularly its "old school" versions. While I've tried to explain each mechanic as clearly as possible, you can consider my ideas as suggestions or house rules you can adapt to your own game.

We're not trying to reinvent the wheel here—just grease it so it runs more smoothly.

 

Overview

Primus, the Prismatic Planet, is a place of wonder and pain.

Its earth is scorched and dangerous. Alien creatures roam the land. People are fractured in many ways, divided into different tribes, cities and kingdoms, each with distinct customs and beliefs. Most have no sense of history and no real grasp of technology, being unable to understand where they come from and how to use the mysterious machines that litter the landscape.

Maniacs, mutants, and marauders, wielding obsidian and bone, ride saurian beasts through the Endless Sands. Psionic monks battle radioactive sorcerers, dinosaurs and warlords in the apocalyptic heat of this lost world.

For now, humanity seems unable to bond together over shared difficulties. Instead, they fight for dominion over scarce resources. Slavery, prejudice and violence are common everywhere.

 


Genre

This setting is inspired by books and other works in the "weird" genre—a blend of fantasy, science fiction, and horror. Its primary influence is sword and planet, a subgenre that typically features swashbuckling heroes, alien worlds, ancient technologies, and a mix of science and sorcery.

This book doesn’t feature orcs, halflings, or faeries. Instead, it offers human-like beings, bizarre alien species, psychic powers, and ray guns. If you’ve read A Princess of Mars or similar pulpy sword and planet adventures (see the list below), you’ll know what kind of world you’re stepping into. If you haven’t—go read them! Or check out the movies, comics, and adaptations. You’re in for a wild ride!

Some aspects of the setting have been directly taken from the public domain works of E. R. Burroughs, H. P. Lovecraft, H. G. Wells, R. E. Howard, and many others.

Many Martian tales have inspired the setting, but the exact placement of Primus in time and space is left to the GM’s discretion. It could be an alternate version of Mars, a distant planet thousands of years in the future, or a world in an entirely different universe.



 

Brief History

The history of the Prismatic Planet before the apocalypse is nearly lost to all living inhabitants.

Legends say humanity was once ruled by the Progenitors, mysterious figures who abused their subjects in various ways, including slavery and scientific experimentation. While some poor humans long for the safety of their brutal masters, most are relieved to be free from their cruel grasp – if they remember these days at all.

The reasons behind the great change are lost or misunderstood in history. It is widely believed that the planet endured a catastrophic event that disproportionately affected the Progenitors. For many days, the sun burned brighter and fiercer than ever before. This mythical calamity is known as The Scorching.

The Scorching decimated vast swaths of flora and fauna, seemingly drying out entire regions—leaving behind empty riverbeds and forgotten ruins, now stranded far from any surviving bodies of water. Entire civilizations may have been destroyed or driven underground into the lost shelters that most surface-dwellers fear to tread. The sun’s radiation remains dangerous even today, but the darkest days of widespread mutation, madness, and destruction appear to be behind us.

Unable to withstand the new, unforgiving conditions, the Progenitors disappeared and relinquished their hold onto the world. In their absence, creatures once kept in check by their dominion flourished in chaotic freedom. Now, the planet is inhabited by disoriented humans, unfathomable alien entities, and savage beasts that no longer fear mankind.

 

The people

We call the ruling species of the planet “humans” for short, though they are something slightly different than humans. In appearance, they resemble people of vivid colors—red, green, blue, yellow, chalk white, and deep ebony. Their physiology is largely human-like, with a few notable exceptions, such as heightened resistance to the planet’s atmosphere and environmental hazards. Whether these traits are the result of genetic engineering or natural selection remains uncertain.

There are many other intelligent species on the planet, such as insect people, robots with varying levels of artificial intelligence, and the mythical progenitors, for example. Humans consider these beings—and sometimes even groups with different mutations, cultures or skin colors—as something other than human.

 

The Planet

Primus is slightly smaller than Earth. In its current state, only about a third of its surface is covered by water. Large bodies of water often contain enormous monsters, and humans are cautious about sailing far from shore with their rudimentary boats and basic nautical tools.

Gravity may be slightly weaker than Earth’s, allowing for larger creatures and taller mountains. For most intents and purposes, however, the inhabitants of Primus refer to it as “Earth,” since they possess little knowledge or understanding of other planets.

Primus has one large moon and two smaller ones. Seasons and day/night cycles are similar to Earth’s. The climate varies greatly but is, on average, hotter and drier than Earth, with extreme cold found only at the poles. Vegetation is scarcer and deserts are more common.

The underground is teeming with caves, tunnels, and abandoned structures—some carved out by creatures like the burrowing prismatic worms, others constructed by Progenitors and other forgotten beings. The underground is often inhabited by creatures searching from protection from the scorching sun and harsh environmental conditions.

The “Prismatic Planet” moniker refers to the colorful nature of its inhabitants. Humans, animals, and plants display an astonishing variety of vivid colors. Even the sky often takes on effects resembling the aurora borealis, which the inhabitants frequently interpret as portents of impending doom.

 

Fauna and flora

The fauna and flora of Primus are markedly different from those of Earth. Mammals—especially domesticated ones—are rare. Dinosaur-like creatures are more common. Many native creatures exhibit a blend of reptilian, arthropod, humanoid, and even vegetal traits. Most species retain symmetrical body structures, although large organisms with six or eight limbs are nearly as common as four-limbed ones. Exceptions do exist and are typically referred to as aberrations.

Animals in Primus are often more aggressive than Earth’s beasts. Since humanity spent years in captivity, animals have not learned to fear them. In addition, the Scorching has made many of them more desperate for food and more willing to fight. Anything larger or more numerous than humans can be extremely dangerous.

The flora also diverges from Earth’s, though plants fulfill similar ecological roles. Their coloration is more diverse: green remains widespread but is not as dominant. Some plants possess limited mobility or exhibit rudimentary telepathic communication, either among themselves or with humans.

It is likely that many of the creatures, plants, fungi, bacteria, and viruses on Primus were genetically engineered by the Progenitors, though humans are unlikely to recognize the difference.

 

Society and culture

Humanity is currently in a savage, sorrowful state. Only a few generations removed from The Scorching, they have little knowledge of what came before—relying only on fragmented legends and half-remembered myths. Prejudiced and superstitious, they distrust outsiders and cling to tribal beliefs.

People are divided into many small tribes and villages, with great cities being exceedingly rare. Communication between settlements is rare and often erupts into violence. While most human groups have learned to survive within the planet’s harsh environment—at least in their small, isolated regions—they remain largely ignorant of its flora, fauna, and even its unpredictable weather.

One trait many people share is a strong sense of practicality. Empiricism reigns—most are more concerned with what they can see (or what can harm them) than with abstract philosophical ideas. Charity, compassion, and self-sacrifice are valued, but not to the same extent as they are by earthlings. Instead, traits like courage, decisiveness, and ruthlessness are prized—qualities that signal one is not to be trifled with.

Charity often serves as a display of wealth, and mercy typically comes with the expectation of future repayment. It’s not uncommon for the elderly to walk away and die alone once they can no longer contribute. Unwanted and disabled children fare even worse.

Religion, likewise, is the worship of the strongest. Local rulers often title themselves as gods. In other tribes, a powerful monster, aberration, automaton or artificial intelligence may be elevated to deity status—knowingly or not. Most cultures lack a clear concept of Heaven or Hell, believing sin to bring doom to themselves or their people in short time. Terms like “god” and “demon” are often used interchangeably to describe incomprehensibly powerful beings. A “god” usually denotes something beyond direct communication, while a “demon” tends to have clearer—though often malicious—intentions, and might even be willing to bargain.

Technology is mostly at a Bronze Age level, with one exception: humans often find and use lost Progenitor devices—though they rarely understand how they work. Most powerful items belong to the ruling class, although any random child can potentially own a small trinket of unknown purpose.

 

Mature themes and the dark side of the prismatic planet

As you can see, life on Primus is far from easy. Humanity engages in many evils—infanticide, slavery, human sacrifice, prejudice, wars of aggression, and the wanton destruction of ecosystems, among others. On top of that, it must contend with man-eating monsters, hostile machines, destructive technologies, radiation poisoning, and severe environmental catastrophes.

This book does not dwell on these themes, though they are mentioned in passing. The bleak setting of Primus need not lead to bleak or hopeless adventures; on the contrary, it can serve as a backdrop for brave characters striving to save the world—or at least their own necks.

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