How does Mad Foam Rager (immediate action) work?

Question

Reading up on Mad Foam Rager, I am not clear how it works. I am wondering if there's clarity somewhere, such as use cases, or errata or I'm just confused about immediate actions or the word "effect". Specifically it's not clear to me when you can inact it, which seems to be the whole point of the feat. In the most complicated games I've played that involve a stack, there is always some point where you cannot respond and simply have to deal with what happened. I think "when" is what I'm missing.

In my use case, the character I am envisioning is a pure barbarian (level doesn't matter I think, let me know if you disagree) with no spellcraft or literacy even.

The benefit:

When fighting, you can endure tremendous blows with little visible effect. As an immediate action, you can choose to delay the effect of a single attack, spell, or ability used against you. The damage or effect does not take hold until the end of your next turn. You can only use this ability while under the effect of your rage or frenzy ability. You can activate it once every time you use your rage or frenzy ability.

Here's some questionable scenarios (can character mad foam past these?):

1 - post hit (critical)) Character is critically hit and the crit is confirmed. This is the simple scenario (beyond just being hit) I am assuming this is yes.

1.5 - post critical effects: Character loves damage and takes the crit but the attacker has a prismatic burst weapon which teleports the character to another plane. On discovery of that teleportation happening, can only that effect be delayed or can the crit (including the damage) be delayed?

2 - post spell (save)) Character with a phobia of fluffy bunnies is hit with Phantasmal Killer and not knowing why the horde of bunnies is climbing on him risks a saving throw and fails. He is informed on failure he is dead. Can he reactionarily mad foam or is post save too late? (I am pretty sure here death is the "effect" but getting less sure)

3 - post spell (damage type)) Character has vulnerability to fire so does not want to take fire damage. Character is hit with a scorching ray. He receives 16 fire damage. Does he now know (no spellcraft) it's fire damage to mad foam?

4 - post hit (secondary grapple)) Character takes an AOO from a constrictor snake and damage is rolled and deducted from HP total. Then the constriction (improved grab) happens, character does not want to be grabbed does he mad foam now? Does doing so now also rollback the damage? Or does he mad foam after a failed grapple check (giving a chance for him to succeed and avoid the effect and save his mad foam?)? Is it his choice?

4.5 - post hit (tertiary constriction/damage)) What if in this same scenario, he forgets he had mad foam and fails the grapple then the constriction damage kills him. Can he mad foam to avoid said constriction or does the mad foam undo the entire event?

(4.75/bonus question: I am also curious what happens if you are not around the snake the next round to be grappled)

5 - post hit (unknown effect that impedes original action)) Similarly, character charges a giant with Hold the Line and is struck on an AOO. After taking damage, character finds out he is "held". Can he mad foam letting him through the charge? Does he just foam through the feat "effect"? Or is it too late once he accepts the hit not knowing the consequences?

6 - post (aoe) spell: Maybe back to simple but the characters group is hit with a fireball. "Used against you" does not seem clear in regards to aoe, but I am assuming the fireball could be mad foamed since you're an included target but only for the barbarian and not for any comrades. In other words, any mad foam usage applies to self as a target and not to spell.

I'm sure there are more (complicated) scenarios but hopefully this gets my confusion across. I personally think the simple adjudication would be just to stop the entire event once the character has the knowledge (feeling fire burn, feeling giant hold you) but especially with multi-part events it seems grey. I am also curious if others would adjudicate that way, if they believe the character then knows what will happen (e.g. "I'm about to die", "I'm about to burn", "I'm about to be grappled", etc.).

If all these scenarios seem Mad Foam-able, if you can think of any more complicated scenarios that wouldn't be, including that in your answers would likely help me.

Before anyone answers "ask GM" my intent/hope is to get opinions, or more hopefully facts, in advance from the group to give to my GM(s) to help guide them if questions do arise and to be guided myself.

Answer 1

What the game also says about Mad Foam Rager

The only additional commentary on the feat Mad Foam Rager (Player's Handbook II 80) that I'm aware of is from the Dragon #351 Sage Advice column "Official Answers to Your Questions" that includes these exchanges:

• When do I activate Mad Foam Rager…—before or after I know the effect that I’m delaying?

  After. Effectively, activating the feat “interrupts” the effect, delaying it until the end of your next turn.

• Does activating Mad Foam Rager… allow me to delay rolling a saving throw (which might let me activate some effect that grants a bonus on the save)?

  No. The feat doesn’t delay the save, just the effect of the save’s success or failure. If an enemy cleric casts sound burst next to you, you’d roll the save normally, then choose whether or not to activate Mad Foam Rager to delay the effect of the spell until the end of your next turn. (81–2 and link added)

(The Sage at the time is Andy Collins. These exchanges are repeated nearly verbatim in the Main FAQ (42), with which some folks have concerns; see here.) This doesn't address precisely the question's issues, but it helps address many of them.

How one DM runs Mad Foam Rager

In this DM's campaigns, after a raging creature that possesses the feat Mad Foam Rager is made aware of the entirety of the impact an attack, spell, or ability—its effect—, then the raging creature may opt to take an immediate action to realize the benefit of the Mad Foam Rager feat therefore delaying for 1 round the cumulative effect of that attack, spell, or ability. Imagining running the feat this way should go a long way toward addressing the issues the question raises, but more detail is offered below.

• The DM tells the rager's player the outcome of the attack—including the outcomes of any additional effects that stem from the attack—, and the player can opt to have his rager take an immediate action to delay that attack's cumulative effect. This includes, for example, dealing sneak attack damage; computing the outcomes of any magic weapon special abilities; employing the feat Stunning Fist (Player's Handbook 101); making now any saving throws against a poison lacing the weapon as well as, if the save's failed, the effect of that poison's primary damage upon the rager.

  Improved Grab: This DM would inform the player of the result of a constrictor's attack—including the result of the improved grab ability and subsequent grapple and constrict outcomes. This DM would politely explain that while the rager could delay solely the improved grab ability's effect just to see what would happen, for the sake verisimilitude the DM would much prefer that the rager delay the result of the natural attack that led to the constrictor's use of the improved grab ability! Refusing this advice makes this scenario kooky quickly, the rager perhaps dragged across the battlefield by a constrictor snake's delayed invisible, intangible tether… or something.

• The DM tells the rager's player what will become of the rager because of the spell or ability that will affect him, and the player can opt to have his rager take an immediate action to delay for 1 round that spell or ability's effect on the rager. This totally includes, for example, the damage that would be dealt by from the 3rd-level Sor/Wiz spell fireball [evoc] (PH 231) or the damage or death that can result from the 4th-level Sor/Wiz spell phantasmal killer [illus] (PH 260).

  Keep in mind that the 2nd-level Sor/Wiz spell scorching ray [evoc] (PH 274) doesn't itself directly affect the rager; the spell's effect is a ray that's used by the caster to make with it an against the rager. While that's kind of nitpicky, it's as important a distinction to the rager as being attacked by a foe that's using the feat Manyshot (PH 97). That is, while only one action is being taken by the foe, the foe's making multiple attacks, and the Mad Foam Rager feat's benefit can be applied to only one lone attack.

To be clear, whenever a raging creature that can still employ the benefit of its Mad Foam Rager feat would be subject to an attack, spell, or ability, it may gain information—that it may be able to, for a very short time, subsequently share—about that ability, attack, or spell that it wouldn't otherwise learn. However, to be fair, if the creature doesn't use the benefit of the feat Mad Foam Rager, it's going to suffer the ability's, attack's, or spell's effect now, and, if it does use the feat's benefit, it's going to suffer the ability's, attack's, or spell's effect anyway 1 round from now.

Further, this does not mean that the raging creature learns, like, the exact name of the ability, attack, or spell or, for that matter, any other details like a spell's caster level, a foe's HD, the precise magic weapon special ability, a magic weapon's magic enhancement bonus, an attacker's base attack bonus, and so on—and especially not an effect's duration! For example, the DM tells the rager that the spell will leave him deafened, not that a sound burst spell will deafen the rager for 1 round. Likewise, on a failed saving throw against the poison on a poisoned dagger, this DM would have the rager learn the poison's initial damage but not its secondary damage. The creature knows only what will happen to it now—or what will happen to it 1 round from now if the Mad Foam Rager feat's benefit is used—but usually not, like, what an ability, attack, or spell is; who used, launched, or cast it; or how long any effect will last. (Obviously, though, the rager's own senses and experience still provide their normal clues.)

This can be complicated in play: An example

On her turn, Yrgnami, a dwarf barbarian that possesses the feat Mad Foam Rager, takes a free action to activate her extraordinary ability rage. Yrgnami then takes a full-round action to make the special attack charge, using her speed to move 15 ft.: 5 ft. normally then 5 ft. into the area Nosrepllat the ogre threatens, then 5 ft. out of one square and into another Nosrepllat the ogre threatens, this last provoking an attack of opportunity from Nosrepllat. Nosrepllat, due to the feat Stand Still (Expanded Psionics Handbook 51), makes a special attack of opportunity against Yrgnami. Nosrepllat's attack of opportunity succeeds and she rolls damage sufficient so that the dwarf must make a Ref save (DC 40). Unsurprisingly, Yrgnami fails.

DM: The ogre's attack of opportunity deals no damage, but Yrgnami's movement stops 5 ft. from the ogre rather than adjacent to the ogre, and her movement's expended.
PLAYER: I'm raging so I take an immediate action to employ the benefit of the feat Mad Foam Rager to delay that attack's effect for 1 round.
DM: Okay, Yrgnami's adjacent to the ogre, but she won't be able to move on her next turn.
PLAYER: [Evil grin.] I'm not going anywhere.

So, yes, this is more complicated than normal and will likely eventually require some ad hoc adjudication, especially if the campaign continues into high levels and the PCs' enemies' abilities, attacks, and spells get more and more complicated. Nonetheless, a feat like Mad Foam Rager is still less complicated than many spells. And it's one of the few sort-of nice things that warriors can get that casters typically can't. I mean, the ability, attack, or spell may still totally kill the rager, but with the Mad Foam Rager feat that's next round's problem.

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Note: The 3.5 revision made it so that, technically, a typical creature—even one that possesses the extraordinary ability improved grab—can't execute a grapple when making an attack of opportunity; see here. Also, the latest printing of the feat Hold the Line from Shining South (20) doesn't halt a struck charger. (This is why the example uses instead the feat Stand Still.)