How does Mad Foam Rager (immediate action) work?

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.