Immunities, Weaknesses and Resistances

If it's highly thematic for a creature to have an immunity, weakness, or resistance, consider adding it. The Resistances and Weaknesses table lists the ranges for weaknesses and resistances by level.

Immunities are generally reserved for creatures made of an unusual substance (like a fire elemental being immune to fire). You can also give an immunity if a creature's biology or construction would logically cause it to be unaffected (like a mindless creature's immunity to mental effects). If the creature should be hard to affect with something but the conditions above aren't true, give it a resistance instead. For instance, most cosmic creatures aren't actually made of ice, so it wouldn't be immune to cold, but its life in space makes it resistant to cold. You'll typically use the lower end of the value on the Resistances and Weaknesses table for a broad resistance that applies to a wide range of effects, like "physical 5 (except silver)" and the higher end for something narrower, like a single damage type. A creature with a resistance, especially a broad resistance or a physical resistance, usually has fewer HP.

Giving your creature a weakness adds flavor to it and greatly rewards effective player tactics once your players identify the weakness. The weakness should apply to one damage type or phenomenon and use the high end of the scale. Creatures typically have at most one weakness. If a creature has a weakness, especially to something common, give it additional HP. The amount of additional HP might depend on how tough the creature should feel if the PCs don't exploit its weakness; a tough creature might have additional HP equal to quadruple the weakness value. A creature with a hard-to-exploit weakness might have additional HP equal to the weakness value or less.

In Starfinder, PCs have access to a wide variety of damage types. A 1st-level character can pack a laser pistol (fire damage), a sonic rifle (sonic damage), or even a neural lash (mental damage). Because of this prevalence of damage type accessibility, resistances and weaknesses can often turn the tide of a battle. Some damage types, like fire or cold, often appear as obvious use cases for resistances and weaknesses. Be sure to vary your creature design to include some that might have mental or sonic resistance as a means of encouraging weapon diversity.

The combination of more HP and a weakness has a different feel from standard HP with resistances. If the creature being an impervious tank really fits its theme, use a resistance with an exception, such as "physical 5 (except silver)." If, however, it makes more sense for normal hits to get through and the creature to simply have great staying power, use more HP and a weakness. Living hardlight and tech zombies are a good example of the difference between these styles. Living hardlight has resistances because they're holograms and hard to hurt. Tech zombies, on the other hand, have more HP and a weakness to slashing damage-they're tougher, but their bodies aren't built to deflect weapon attacks, and slashing attacks can rip them up quickly.