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Chapter 2: Tools / Building Creatures / Design Abilities

Reactive Abilities

Source Gamemastery Guide pg. 69
Reactions and free actions with triggers can give a creature an impact outside its turn. This can make the fight more interesting, but may 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, an ogre doesn’t have Attack of Opportunity because it’s a big oaf. 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’ll 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 an incredible duelist or something similar.

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.”

Reaction Damage

Source Gamemastery Guide pg. 69
Reactions should use lower damage, usually that of a moderate Strike. A reaction that deals area damage might deal low damage, though use such reactions with caution.