OSR: Magical Industrial Revolution - US/NA Copies

Even more goods news! Print copies of the acclaimed Magical Industrial Revolution are now available in the US / North America region. Check out Indie Press Revolution's store.
For a variety of reasons, the US postal system is in turmoil right now, so expect delays, unusual costs, etc. These are interesting times. Be prepared to pay an interesting price. For UK/EU copies, check out the SoulMuppet store.


Sci-Fi: Alien Scale in Space Opera

In most space opera settings, aliens are human-sized. A "giant" alien might be all of 9' tall; small ones tend to bottom out at 3'. In media with budget constraints, this is fine. You need to be able to fit an actor into the rubber suit. But RPGs have no budgets.

For reasons of convenience, humans might associate with similarly-scaled aliens (with similar atmosphere, gravity, pressure, etc. requirements), but there's no reason that has to be the absolute limit. "Bleeds green blood and has two hearts" is barely weird biology.
Note: the obscure string of letters and numbers attached to each species is explained in this post.
The inspiration for this post was a comment from Nobodi12.
But this categories face the challenge of " If everyone has to wear miniature spaceships to visit each other, it's not space opera. "

If we can't survive in the same atmosphere the kicks one get out of aliens are much minor. As a player I would have less fun due to limited interaction with aliens. It makes barriers and making interesting NPCs is already hard. Worse if they have to be PCs. Size as well, anything more then 1 order of magnitude different then a human becomes a McGuffin/Boss monster and not something you routinely interact with.
And they are right. Anything significantly bigger than a human is a threat, or at the very least unnerving. (Dragons, whales, etc.) Anything significantly smaller is adorable or possibly creepy (spiders, mice, butterflies, etc.). We're very focused on our own scale.

Let's look at a few examples from the 1c (1 cognitive-speed-equivalent to human, i.e. people you can carry on a real-time conversation with) range. How could a GM use them as NPCs? How could they use them as PCs?

The Central Vreen

G - H2 - -100/200/600oC - 0/0.02/0.3atm - 0/2/5g - N# - 1000m - 1c - IS - BR5
The Central Vreen resemble transparent sea jellies. A typical mid-life roving unit (as opposed to a juvenile, an instar, or a sedentary late-life retirement unit) is around 1km long. They are therefore at the upper end of individual-social life in general. (Colony-units, vacuum-dwelling film-envelopes, and some geomorphs can grow to orders of magnitude larger.)

They are very wealthy for three reasons. First, any Central Vreen ship is, by necessity, enormous. Decommissioned personal shuttles are occasionally used as bulk transports or space stations. Second, they live for a very long time by most galactic standards, and can molt to a previous stage if the situation requires it, giving them effective immortality. They build structures, both political and economic, to last. And third, they have a knack for social adaptability, fitting their requirements to the needs or biases of other species.

(A fourth theory, put forward by a few eccentric xenobiologists, states that the Central Vreen like to acquire and cultivate smaller life forms as a throwback to their original forms as the backbone of living gas giant "reef systems". A healthy "reef" has many "fish".)

Their size and atmospheric requirements make face-to-face meetings with most species impossible. They communicate primarily via radio, with colour-shifting skin patterns for emphasis. The Central Vreen use telepresence screens. Their "faces" are a familiar sight to most diplomats, who occasionally forget that the face on the monitor is the size of the average cargo ship.

But they also use drone-units (known as ROVs or Waldoes). They metallic build to-scale replicas of the species they intend to visit, then pilot them via a distant virtual reality dome. Some use telepresence screens to project the Central Vreen's face, others have featureless masks or simple indicators.

As PCs
A Central Vreen PCs using a Waldoes is, effectively, driving a robot, usually with 360 degree vision (the Central Vreen have full-body photoreceptors) and a tendency to misjudge distances and respective sizes. There's plenty of room to put a human-scale ship on the outside of a Central Vreen hull without anyone noticing, but a Central Vreen ship is comparatively quite fragile.

Melvyn Yeo

The Orlo

G - O2 - -40/30/90oC - 0.1/1.3/3atm - 0/1/3g - P# - 10m - 1c - IS - B

The Orlo are thousand-limbed pale blue beetles the size of a car. Eight gem-like eyes in two rows of four, truly alarming manipulator mouthparts (hidden by a veil), and decorative horns. They are social among their own species, but only after formal introductions and a strict hierarchy is established. Some xenoanthropolgists classify them as forming "#-sized indivisible units" instead, because crews and diplomatic missions can fail completely if a member is removed or added unexpectedly. Other species, thankfully, do not trigger this response.

An Orlo can fit in most human-sized habitats, but smaller space stations and narrow corridors present a problem. They excrete cat-sized semi-parasitic sensory grubs to investigate difficult spaces, then devour them upon their return. The grubs are slightly intelligent, can speak, and can manipulate objects with their mouthparts.

As PCs
An Orlo PC is large, armoured (to a certain extent), and used to biting their problems to death. The exact limitations of a sensory grub are up to the GM.

Finnian Macmanus

The Kursleck

G - O2 - -40/10/30oC - 0.2/0.9/1.1atm - 0/1.4/4g - P# - 0.1m - 1c - IS - I

Kursleck are melon-sized spheres of dense black prehensile hair with two extensible sensory stalks. Upon joining galactic society, they were chagrined to discover most of the species sharing compatible environments were considerably larger than them, and often completely immune to the sound-based stealth tactics the nearly blind Kursleck took for granted. Still smarting from a few ill-advised wars, the Kursleck are slowly finding their place in the galaxy.

To avoid being trampled, modern Kursleck are suspended beneath floating grav discs. The sight of a black furball with a halo, hovering at head height, and sniffing the air with two antennae can be alarming, but seeing eye-to-eyestalk has advantages.

As PCs
A Kursleck PC has massive silent movement bonuses (except against sight) and, if they've got a hover-disc, can fly. Terrible eyesight but excellent hearing, and the ability to hold up to 60 ring-sized objects.

Ariel Perez


G - O2 - -20/20/40oC - 0.3/1/1.3atm - 0/1/3g - P# - 1m - 1c - IS - B

Humans are slightly smaller than average, prefer slightly more gravity, and slightly lower temperatures than their their assigned atmosphere-temperature-gravity band. They are well within the centre of the bell curve; over a hundred species can directly interact with human structures and vice-versa, with a further three hundred species capable of interaction with limited adaptation (extra insulation, limited exposure, scale issues, etc.).

As relative newcomers with a limited technological base, humans tend to use telepresence for most scale-differential interactions, though they can adapt to Waldo piloting fairly easily. Some of their smaller ships are configured to interact with larger gas-giant species directly. Humans have broadly porous social groups, and assign human-like characteristics to inimate objects and non-sentient creatures. If they find a conceptual handle for a new species, they rapidly work out how to interact with them. This can result in disaster, but on average tends to work out positively.


Vague Ideas

1d8 Smaller to Larger Interaction Methods
1 Appropriately scaled manipulator suit or mini-craft.
2 Suspensor platform or hoverchair.
3 Natural flight and quick turns.
4 Coordinated assembly-stack. Highest ranked on top.
5 Stoic acceptance, vivid communication, and high speed.
6 Dedicated porter-species. Possibly a host.
7 Hired porters and local guides, possibly unaware of their role.
8 Holographic adjustable communication-form.

1d8 Larger to Smaller Interaction Methods
1 ROVs/Waldoes. Uniform models, custom-built, or off-the-shelf adaptations.
2 Telepresence and distant guidance.
3 Extremely dangerous temporary dimensional compressor.
4 Dedicated interpreter-species. Possibly mind-linked.
5 Juvenile forms sent to live among other species, growth halted via medicine.
6 Growth into starship- or -transport forms. Live inside one.
7 Temporary budding or subunit/organ detachment.
8 Extruded sensory goop.


Space Out of Colour

A bit of microfiction in the style of Things by Peter Watts.

Massive spoilers below the cut for Colour out of Space (2019) by Richard Stanley.


Sci-Fi: Alien Categorization Codes for Space Opera

Most space opera or soft-sci-fi settings use broad categories of life. "Class M planets" and "Carbon-based lifeforms" are two typical examples.

They are useful shorthands for explaining why everyone looks like a human in a rubber suit and why every planet vaguely resembles California or a quarry in England, but they're not particularly interesting. "Carbon-based" is so vague that it's practically a non-sequitur; it tells you almost nothing about how the creature operates and what environment it requires. Extremophile bacteria, tube worms, spiders, and mushrooms are all carbon-based lifeforms.

I wrote about set-dressing aliens in this post.


  • Infections and cross-contamination are not significant issues. E.g. this fungus from Planet A won't happily colonize human skin, this creature from Planet B doesn't casually emit compounds that are toxic to humans, etc.
  • There is enough overlap that categorization like this is useful. If everyone has to wear miniature spaceships to visit each other, it's not space opera.
  • Species are abundant and have reasons to interact. This guide isn't useful in a setting without thousands of potential intelligent species. Some sort of galactic community is required.
  • Interspecies communication is possible (i.e. it's possible for two species to communicate using the same language.) Sure, one of them might use radio and the other might use gestures, but it's possible to build a grammatical base that means something to multiple species.

Categories are listed from most to least crucial. If you're an alien scooping up a creature or sorting out accommodation and compatibility, you'd work from the top down. They're sort of like taxonomic ranks.


The phase (or phases) a creature requires to live. Not the phases it can safely inhabit (e.g. swim in), but the phases that are required for life.
  • Gas Phase
  • Liquid Phase
  • Solid Phase
  • Plasma Phase (?)
  • Vacuum
Humans are G-, amphibians are GL-, fish are L-. Solid Phase creatures are difficult to imagine, but maybe some sort of distributed high-pressure network of tendrils or self-propagating migratory crystal patterns (like rock-prions). Plasma-phase creatures presumably live in the heliosphere of stars, the upper atmosphere of planets, or other equally odd locations. 

Primary Energy Exchange Element

The stuff a creature needs to live on a minute-by-minute basis. For setting purposes, the atmosphere the creature breathes.

It might be more useful to phrase this in electron donor/acceptor sets (e.g. humans would be hydrocarbon+O2 / CO2+H2O, hydrogen bacteria would be H2+O2 / H2O, etc.) but the list would be enormous and unwieldy for soft sci-fi or space opera games. You should still check out the list of real chemolithotropes. Life is weird.

Energy requirements (light, electricity, neutrons, etc) are best categorized with Optimal Radiation (below).

  • O2
  • CO2
  • H2O
  • H2
  • CH4
Humans, dolphins, and fish are -O2-. Plants are -CO2-. Creatures on Titan might be -CH4-.
lifeslittlemysteries.com (defunct)


In setting, this is probably expressed as a single operator or symbol (some sort of compressed ideal gas law thing)

Temperature is given as a 3-point range: minimum, optimal, and maximum. The value is calibrated around environmental temperature. Clothing is assumed; external heating or cooling sources (fire) are not. For humans, a range of -20/20/40 oC is close enough to accurate.

Pressure is also given as a 3-point range: minimum, optimal, and maximum. For humans, a range of 0.3/1/1.3 will do.

(Pressure is tricky; humans can breathe in a 100% oxygen atmosphere, but atmospheric oxygen is around 20%. At 100% O2, humans can survive around 1 atm of pressure, but at 20%, we can survive up to 2.5 atm of pressure. And, of course, temperature ranges vary with humidity...)


Again, given as a minimum, optimal, and maximum range. Humans can operate in freefall, and the maximum feasible gravity seems to be 3-4g, so 0/1/3g.

I'd expect most creatures that can survive falling or rolling for any length of time to be able to survive in 0g environments. Pitcher plants couldn't.

Optimal Radiation

The assumption is that the creature requires this level of radiation, but should be shielded from all other forms. Deriving a numerical value here starts to cross the line between "back-of-the-napkin RPG math" and "actual physics". I couldn't make it interesting.

Humans need Photons of energy X to energy Y, with a radiant energy density of Z. So -P#-
High-altitude gas giant creatures might need Neutrons of energy A to B with a radiant energy density of C. So -N#-
Creatures which have no specific radiation needs (e.g. prefer darkness) are denoted with an X.

It's interesting to note that the sun's output is not evenly distributed across all wavelengths. Without some sort of intensity curve, the "default" light in a room will never be a typical sunlight white.

Ivan Khomenko


Even if creatures have all the above characteristics in common, building structures that can accommodate a variety of scales is useful. For space opera purposes, size bands based on orders of magnitude (0.1m, 1m, 10m, etc.) are probably acceptable. Or maybe there's some sort of convenient clumping principle at work, and intelligent life tends to occur in narrow bands around "about shrew sized", "about person-sized", "about whale sized", etc.

Cognitive Speed

How quickly the creature can communicate a fixed packet of information to another creature, or perform a standard quantity-rearrangement or pattern matching test. Computers have a value thousands of times higher than a human. This is another order-of-magnitude range; 0.1c, 1c, 10c, where c is an arbitrary anthropocentric value.

For a space opera setting, it's probably easiest to assume everyone sharing an environment has a comparable cognitive speed, but it might be interesting for some creatures to operate in very different ways.

Social Organization

A series of codes for typical groups.
  • Individual Asocial (-IA-)
  • Individual Social (-IS-)
  • Collective of size # to # (-C#-#-)
  • Hive of size # to # (-H#-#-)
  • #-sized Indivisible Unit (-#U-)
Basically, "how many can we put in this tank before they start fighting or die of loneliness?"


A strange code, but I suspect creatures with similar symmetry plans tend to have broadly compatible views of time, design choices, etc.
  • Radial #
  • Bilateral
  • BiRadial #
  • Icosahedral
  • Asymetric

Dominic Qwek


I've had to eyeball a few values. Nobody, as far as I know, has ever put a whale into freefall.
  • Humans are G - O2 - -20/20/40oC - 0.3/1/1.3atm - 0/1/3g - P# - 1m - 1c - IS - B
  • Blue Whales are L - O2 - 4/12/20oC - 1.5/3/10atm - 0/1/1.5g - P# - 10m - 1c - IS - B
  • Ants are G - O2 - 10/30/40oC - 0.2/1/3atm - 0/1/3g - P# - 0.01m - 1c(?) - H100-2000 - B
  • Titan Spiders are G - CH4 -  -190/-180/-120oC - 0.7/1.5/4atm - 0/0.1/0.6g - X - 1m - 10c - IS - R8
  • Hydrogen Rays are G - H2 - -80/200/500oC - 0/0.01/0.1atm - 0/2/6g - N# - 100m - 0.1c - IA - B


In a setting like this, I'd expect compatible species to form parallel galactic civilizations. The oxygen-breathing approximately 1g people might have their own wars, only vaguely aware of the politics of the methane-breathing 0.1g ice-worlders. Intermediate or interpreter species are probably valuable. Collaborative space stations probably feature a wing for the most common or influential types, plus a neutral zero-g zero-atmosphere area.

This guide also helps colony building. A survey team can scan a world, generate the correct codes, and then figure out what species might be interested in visiting. Jupiter could be a tropical vacation paradise. Humans can't use it, but could trade access or ownership rights. It's much easier than terraforming. Instead of fixing Venus, sell it to someone who likes it as-is, or just needs to make a few tweaks.

Humans have an incredibly tiny livable range on every axis. We're used to taking oxygen, pressure, and temperature for granted because that's how space opera works. Push any value outside the habitable range and everything falls apart.

Mass and special requirements are a real pain. If dolphins built the Saturn 5 and wanted to land on the moon. Assuming they ate the same amount of food, consumed the same amount of oxygen, and took up the same space as the 3 human astronauts, they'd still need to haul an extra 36,000lbs of water into space, effectively doubling or tripling the payload. And because of the tyranny of the rocket equation, that means a much bigger rocket. Still plausible, but inconvenient. Then again, vacuum-adapted creatures probably laugh at humans hauling all that neutral gas around.

It's best to pack your own food (or food additives). Gene-tweaked humans can probably get by with a small pack of pills and requests for water and glucose, but it's not exactly high cuisine.

Each species needs to have its own experts. The life science technology of one species, no matter how advanced, might do absolutely nothing for the next species. First aid and emergency triage (e.g. basic medieval medicine) is probably cross-trainable, but everyone should carry their own first aid kit, ideally with instructions. Aliens can sell us a better microscope or fab up a few thousand litres of morphine, but they're probably baffled by white blood cells and drug interactions.