Does PC have to be aware of being targeted to use immediate action as a response?

Question

Question as simple as title yet very hard to answer. I'm specifically referring to things like:

• Abrupt Jaunt variant wizard class feature,

or

• Wings of Cover spell,

or any other similar effect.

Can player use one of those in response to attack that he/she either can't perceive or doesn't know where will land? For example:

• Fireball (PC doesn't know where it hits until it hits, even if player does),
• Ranged attack (PC doesn't know whether he is being targeted or his teammate right next to him, even if player does),
• Sneak attack (PC doesn't know the attacker exist at all before being hit).

Answer 1

We just don’t know.

The rules for immediate actions (and other triggered actions, e.g. readied actions) just aren’t detailed enough to answer these questions. These are questions for your DM, not us.

Certainly, if you always have perfect awareness of opportunities to use immediate-action effects, that gets a bit god-mode (particularly with abrupt jaunt), but if you have no awareness, they quickly become useless, so a DM is going to have to find some middle ground. In practice, that’s almost certainly going to be an ad hoc “I know it when I see it” sort of situation, because foreseeing every possible scenario is impossible. Still, it can be possible to discuss and establish guidelines beforehand, so that a player has a reasonable ability to predict when they will and won’t be able to use such abilities.

But you won’t find such guidance anywhere in the rules.

Answer 2

Contrary to another answer, this seems to be reasonably straightforward.

I'm going off the top of my head, so please feel free to point me the errors of my ways.

Abrupt Jaunt is an immediate action. Immediate actions cannot be taken while flat-footed. If a character can not perceive an attack, he is considered flat-footed vs that attack. Hence, no immediate actions to get away!

In your examples:

• Fireball is something you CAN evade via jaunt, because in general in combat you're considered aware of your surroundings and tactical situation. The usual exceptions apply: fireball in the surprise round, invisible caster, etc, etc. See also: reflex saving throw, representing the person actively trying to get away. If you get a reflex save, you are aware enough to have an option of taking an immediate action.
• Ranged attack goes along the same line of reasoning and you CAN evade it. See also: dodge and dex bonuses to AC, representing the person actively trying to get out.
• Sneak attack goes along the same line of reasoning and you CAN evade it: you know it's there, you're just too busy with something else to protect your vulnerable spot. Do note that a surprise attack would NOT be evadeable, but not every surprise attack is a sneak attack and vice versa.

Please note that this, while permissive, is still far from the god mode: you only get one immediate action per round, and have to jump through hoops to get more.

Link to the immediate action definition that mentions "no go if flat-footed": https://www.d20srd.org/srd/combat/actionsInCombat.htm#immediateActions (Any better links are welcome)