Design Abilities

There are a few principles of ability construction that you'll want to keep in mind. Some guidance for specific types of abilities will come later, but these apply to everything.

• Respect the action economy.
• Make sure abilities are level appropriate.
• Avoid “invisible abilities.”

Abilities a creature uses on its turn have the most flexibility and scope. You can use the Spell DC and Spell Attack Modifier table on to determine active ability DCs as well as spell DCs. You can have an ability use 1 to 3 actions as needed (or be a free action in rare cases) and use just about any type of tactic. Feats, spells, and existing creature abilities provide a wide variety of examples, so look for something similar to your idea to use as a basis.

Consider how you want your creature to spend its turns. Two-action activities pretty much define the creature's turn, and single actions work best for supplemental benefits or normal Strikes. As you build out your idea of a creature's turn, don't forget about movement! A creature often needs to spend actions getting into position, especially early in a fight. This is especially challenging with melee-focused creatures. You can give such creatures abilities similar to a solarian's Stellar Rush or the void shark's Atmospheric Breach, or even grant it abilities that function like augmentations or armor upgrades from Player Core.Use 3-action abilities sparingly, as a creature can't use them if it's slowed or stunned—making a creature's coolest or most defining ability use up 3 actions might mean the creature never gets to use it. These activities should be reserved for abilities that include some movement (like Trample) or that the creature is likely to use before engaging in combat. Don't make an ability use 3 actions as a way to balance it—saying “This can be more powerful than other abilities because it is less likely to work,” is a recipe for frustration if you've made a cool ability that's too hard or even impossible for the creature to use.

Be especially careful with activities when designing boss creatures. They're likely to get targeted with the PCs' most powerful detrimental effects, get grabbed, become slowed, or otherwise have their actions restricted. Bosses need to have solid options they can use with 1 or 2 actions. This lets them use their remaining actions to get away, use a simple ability, or otherwise keep the fight dynamic.

Active offensive abilities usually fit creatures better than defensive abilities do. Save defense increases for creatures that are strongly defense-themed. For martial creatures, something as simple as a shield and Shield Block is usually plenty. Defensive abilities often run the risk of being invisible abilities. For examples of good defensive abilities, look at spells like sanctuary for ideas, or other spells that create interesting protective effects instead of just granting a bonus. If you do want to make a creature defensive, pick one defensive ability rather than several, since stacking up multiple defenses can make for a frustrating fight. One solid style of defensive ability is a mode switch, which causes the creature to get stronger defenses but limits its attacks, spells, or other offensive options.

Reactions and free actions with triggers can give a creature an impact outside of its turn. This can make the fight more interesting, but it might also be risky. It's tempting to give every creature a reaction, but that's not necessarily a good idea.

To decide whether your creature should have a reaction, first consider if the creature has the reflexes or insight to react well in the first place—for instance, a scavenger slime doesn't have Reactive Strike because it's slow to react. Oozes, constructs, and unintelligent creatures are less likely to have reactions than others for this reason.

Second, look at the complexity of the encounter your creature is likely to appear in. If you have a large number of creatures, skipping reactions can make the fight flow faster. A creature that's more likely to fight solo, on the other hand, might have a reaction to give it a way to continue to be dangerous amid an onslaught of attacks by the party.

When creating reactions, be careful with “gotcha” abilities—ones that punish players for making perfectly reasonable choices, for rolling poorly, and so on. If you include abilities like this, they need to reinforce the creature's core theme and the play style you want it to use in combat. For example, a creature that Strikes as a reaction when someone fails an attack roll will encourage PCs to use their actions on other tactics, rather than attacking multiple times each turn. Is that what you want? Is this dynamic essential for making the creature feel like it's supposed to? This isn't the type of ability you'd give to any old creature—only a skilled melee combatant.

Reactions should require something out of the ordinary to happen, or should be relatively weak if triggered by something ordinary. A reaction that triggers anytime someone tries to Strike a creature is likely to be perceived by the players as uninteresting because it's so predictable.

The best reactions should be telegraphed so when they happen, it makes sense to the players. Think of one of the core reactions of the game: Shield Block. The creature raises its shield—an obvious action the PCs can see—so when it blocks damage from an attack, that makes perfect sense. Similarly, if you made a crystalline creature, you might have it build up sonic energy in a low thrum, so when it uses a reaction to release a burst of sonic energy when hit, the players can say, “Oh, I should have seen that coming.”

Certain abilities shouldn't use any actions. Auras are a common constant ability, with frightful presence, the pachinyam swarm's dust cloud, and the bloodbrother's frigid cold as notable examples. An aura needs a range, and if it needs a DC, you'll usually set it to the moderate spell DC unless the aura is one of the creature's defining concepts. For example, the liberoba's ultrasonic pulse DC is significantly higher because the aura is such an iconic part of the creature and necessary for it to see enemies.

Abilities the creature has no control over should be automatic. For example, the cybernetic zombie explodes when it dies. It has no option not to, so this wouldn't make sense as a reaction or free action. Conversely, the Ferocity ability is a reaction because it requires the creature to give itself a last push to stay at 1 HP.

A skilled creature might have abilities related to its skills. The skill feats in Player Core make for a good baseline. Avoid giving your creature skill abilities that won't matter in its interactions with PCs.