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D&D 4E actually took a logical step to clarify not just spells but other abilities as either an interrupt (it gets resolved before someone else’s action, like an attack of opportunity) or a reaction (it gets resolved after). Pathfinder kept immediate actions as usually behaving like an interrupt and so did D&D 5E (though it switched to the term reaction).
In our ongoing quest to simplify and clarify rules language, we’re going with reaction in Corefinder, and in the interest of streamlining and codifying rules, we’re also combining attacks of opportunity as a type of reaction rather than this oddball standalone resource. Most creatures that take AoOs don’t usually have other options of things to spend their immediate actions on, since most of those things have lived on the spellcaster side of things in Pathfinder.
We’re addressing that disparity in several ways. For one, we’ve added lots of new reactions that anyone can use. We’ll talk more about those next time.
In addition, some classes and creatures that might have occasion to use multiple attacks of opportunity will have ways to get them, though for the sake of smoothing out gameplay, those won’t be as extreme as some PF1 AoO-heavy character builds now.
Attacks of Opportunity
Most attacks are something you do on your turn, but some actions an enemy takes may cause them to let their guard down or act recklessly, allowing you an opening to attack them as a reaction rather than having to wait until their turn. This is called an attack of opportunity (AoO). An attack of opportunity is resolved immediately before the action that provokes it, and as a result it may interrupt and spoil that action, such as by breaking a creature’s concentration or even incapacitating them before they have a chance to complete the action that provoked your AoO. Certain conditions must be met for you to take an attack of opportunity.
You Must See the Target: If you cannot clearly see the target, you cannot take AoOs against them. This is true even if you know the target is present and even know which square(s) it occupies.
Precise Senses: Some creatures have exceptionally acute senses that allow them to effectively “see” a creature with a sense other than vision, allowing them to take AoOs against them.
You Must Threaten the Target: A creature must be within your reach, and you must be armed. For most Medium creatures, that means the target must be adjacent to you.
Cover: When there is an obstruction between you and a target, they have cover from you (see page xx), which grants them a circumstance bonus to their AC. The bonus depends on how much protection that cover provides. Cover can be provided by creatures or objects that are in the way of your attack. Cover provided by another creature, whether an ally or another enemy, is called soft cover, while cover provided by an object is called hard cover.
While you can attack a creature with any type of cover (other than total cover), if there is hard cover between you and another creature, you do not threaten them and their actions do not provoke AoOs from you.
Your Opponent’s Action Must Provoke: Many actions are just an ordinary part of combat and do not expose a creature to an AoO. The two most common actions that can provoke an AoO are movement and complex actions.
Movement: When a creature moves out of a square you threaten, you can take an AoO, targeting them immediately before they leave that square. In addition, certain other move actions provoke AoOs, as described on Table 7-X.
Complex Actions: Some actions require intense focus and concentration, or simply pull your attention away from protecting yourself on the battlefield, that they leave you open to attack. Table 7-X indicates actions that provoke AoOs.
Multiple Attacks of Opportunity: If more than one creature threatens a creature when it takes an action that provokes, each threatening creature can take an attack of opportunity.
Since you normally can have only one reaction at a time, you normally can take only a single attack of opportunity each round. However, some creatures have the ability to take additional reactions that can be used only for attacks of opportunity per round. If you have that ability, you can take an AoO each time a creature you threaten performs an action that provokes one. However, each provoking action provokes only a single AoO.
For example, if a creature moves through more than one square that you threaten, you can take only one AoO against them, for the first threatened square that they leave. However, if that character stood up from prone, then moved out of a threatened square, then made a ranged attack while still in your threatened area, you could potentially take three AoOs against them, once for each action.
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