As we all know, immediate actions are just like swift actions, but can be performed outside of one's turn.
However, unlike a swift action, an immediate action can be performed at any time – even if it's not your turn.
However, it is still unclear if one can use an immediate action during someone else's action.
For example:
A monster swings at a conjurer.
- Can conjurer abrupt jaunt outside monster's reach right after the attack was rolled, thus wasting an attack?
- What about right after the damage was rolled, but not yet applied?
- What about casting celerity and baleful transposition on yourself and monster's ally so the monster would hit his ally, given high enough attack roll?
Let's complicate a bit with a complex, full-round action on a monster's side.
- Can one use immediate action in between attacks in full attack?
- What about after movement part of a charge?
Best Answer
All about Immediate Actions
An immediate action, according to the SRD, is used as follows
And that's pretty much it.
An immediate action isn't like taking a standard action to ready. An immediate action can't be taken in response to another event then occur before the event it's responding to. There's no last-in,-first-out in Dungeons and Dragons 3.5.
Further, while some events are viewed as having discrete steps at the gaming table, some of those events don't actually have all those steps according to the game, and therefore must be resolved before immediate actions can be taken.
Unlike many trading card games, there's often no specific declare phases or discrete steps (e.g. a creature doesn't pick a target then make an attack roll then roll damage, allowing responses to each). A creature does something that needs to be resolved (e.g. make an attack, cast a spell) before something else can occur. Immediate actions, then, can't be taken while the other creature has an event unresolved, but an immediate action can be taken between events.
The DM must determine when an event has multiple steps that can be interrupted (during which creatures can take immediate actions) and when an event is finally resolved, but the game provides some guidance.
Event: Attack Roll
An attack roll
Thus once the attack roll is made, an immediate action can't taken until damage is dealt. The attack roll, once made, determines both whether an attack hit and inflicts damage. Note that this differs from Ernir's answer to this question.
Event: Saving Throw
A saving throw is resolved discretely. There are opportunities for decisions during saving throws. For example, "A creature can voluntarily forego a saving throw and willingly accept a spell’s result." This opportunity for decision-making permits immediate actions to be taken when rolling a saving throw (e.g. the psionic power evade burst)
Specific Exceptions
Some special abilities interrupt events that can't otherwise be interrupted. For example, the elan's supernatural ability resilience says, "As an immediate action, an elan can reduce the damage he is about to take by 2 points for every 1 power point spent." If the elan weren't about to take damage from an attack, he couldn't use this ability, so this ability allows the elan to take an immediate action before damage is inflicted during an attack.
Example 1
A monster makes an attack roll versus a conjurer with the supernatural ability abrupt jaunt alternative class feature and who has prepared several spells with immediate action casting times.
Example 2
Consider this text from the 2nd-level Clr spell close wounds [conj] (SpC 48), which has a casting time of 1 immediate action,
The game must make a special case for the spell close wounds because otherwise the spell wouldn't do what the game wanted it to do--keep folks alive. Without that text, the damage would resolve, the creature would die, and the spell close wounds wouldn't be anything more than a weak, off-turn cure spell.