Rarity

Let's first review the default usage for the four rarities in the game and how these already start to tell a story about your universe.

• Common elements are prevalent enough, at least among adventurers, that a player is assumed to be able to access them provided they meet the prerequisites (if any).
• Uncommon elements are difficult to access or regionally specific, but a PC can usually find them eventually with enough effort, potentially by choosing a specific character option or spending substantial downtime tracking them down.
• Rare elements are lost technology, ancient magic, cutting edge biotech, and other options that PCs can access only if you specifically make them available.
• Unique elements are one of a kind, like a specific magical artifact, one-of-a-kind prototype, or a named creature. You have full control over whether PCs can access them. Named NPCs are unique creatures, though that doesn't mean their base creature type is unique. For instance, a shirren named Zazi is unique, but that doesn't mean it would be any harder for a PC encountering her to tell she's a shirren—just to discern specific information about her.

Options of higher rarities aren't necessarily more powerful than common ones, but they might have unusual capabilities with large ramifications for the campaign setting or the types of narrative moments common in a science fantasy game. For instance, the raise dead spell is uncommon, since Starfinder's default setting assumes that the death of important characters, like the leaders of galactic federations or powerful villains, shouldn't be easily reversed by any common doctor or mystic, only those who have specialized knowledge in these complex fields.

Just because something is common or uncommon in one context doesn't necessarily mean it's the same in others. This is specifically true when comparing the commonality of a creature and an ancestry. For instance, while orocorans are a relatively common foe for adventurers to encounter in the Gelid Edge and are thus a common creature, in most settings they're still far less prevalent than humans or ysoki and would be an uncommon ancestry.

Because uncommon elements are available in certain circumstances, they often vary by locale, even within the same solar system. For instance, weapons wielded by soldiers of the Azlanti Star Empire, such as the aeon rifle might be uncommon in the Pact Worlds, but in the Azlanti Star Empire, an aeon rifle would be common and some Pact Worlds weapons, perhaps the aucturnite chakram, might be uncommon. Similarly, in the Veskarium, uncommon vesk weapons like the doshakari might be common. Some items are uncommon everywhere, such as the quasar solarian crystal.

The same is true of many ancestries and alien creatures. While ijtikri and talphi are common in the Veskarium, they're less often encountered in the Pact Worlds. This is particularly noticeable for ancestries who live primarily on a single planet, such as copaxis, or who lack access to Drift travel. Likewise, khefaks are common creatures on Akiton but are uncommonly encountered on Castrovel and are rarely encountered on Vesk-8, though they've infested many desert worlds, industrial parks, and junkyards near and far. Creatures that are native to a specific place are more likely to be found in other places with similar environments.

Similarly, technology levels can be a factor in rarity. Civilizations with industrial levels of technology probably lack access to starships but likely still have machine guns and shock truncheons, while civilizations with medieval levels of technology might treat all Starfinder items as rare or unique and instead use items from Pathfinder in their place. Conversely, PCs accustomed to Pact Worlds level technology who suddenly find themselves on a technologically advanced world will encounter rare and unique items that are common in this new region. Using rarity in this way can help differentiate technology levels for adventures that occur on isolated planets, alternate realities, or in other time periods.

Elements like ancestries, backgrounds, classes, and heritages that a player must select at character creation can still be uncommon or rare. Obviously, there's no opportunity for the player character to search for them during play, but these rarities still indicate the prevalence of adventurers with those elements in the world. You can decide to allow them on a case-by-case basis depending on the campaign and the story your group wants to tell. For instance, a game set in the Szandite Collective might have fonqugon as a common ancestry, while the typical common ancestries are less common. An official player's guide for a Starfinder Adventure might have uncommon backgrounds that you can access by playing the adventure.

You might craft a quest involving an uncommon or rare subject. For instance, players might encounter a force field that requires a rare spell to deactivate and have to travel to a distant planet to learn it. If a player has their heart set on an option that's not common, look for ways to build a story in which their character acquires that option.

With the rarities at your fingertips, you and your group can start building a unique world using rarity as a tool. Imagine a world where one or more of the core classes are rare. Maybe the natural forces of the universe are out of balance, and a PC solarian is one of the only solarians in the galaxy. Perhaps witchwarpers are rare and are hunted by bounty hunters, police, and pirates across the galaxy. For a grittier feel, you could make abilities that can remove afflictions uncommon or rare. You could even create a lowmagic sci-fi setting where all spells and magic items are uncommon or rare.

You can add, remove, or alter Access entries to fit your universe. For instance, if in your universe the creator god is really an immortal fungal colony, you might add an Access entry to raise dead and resurrection for characters who were infected by divine spores. In a campaign where everyone's a lab-grown clone, you might limit Access to one ancestry to start. These are just a few ideas to help get you started. The number of ways you can vary rarities to adjust your setting, story, and game are nearly unlimited.