Unfortunately, D&D uses the word effect rather confusingly (namely, as a synonym for "game mechanical cause" and
not for consequence). If you read the example provided in the Saving throw section, it's clear how they intend the word "effect" to be interpreted. "Another kind of effect is like an imp's hellish poison, which includes both ongoing poison damage and a -2 penalty to will defense."
That's not brilliant use of the English language, but it's consistent with how the word effect is used elsewhere in D&D (and not just this edition, either).
The entire quote (I hope this is still OK by the guidelines):
Each round, at the end of your turn, you roll a saving throw against each effect on you. Sometimes an effect is a single condition or one type of ongoing damage. Another kind of effect is like an imp's hellish poison, which includes both ongoing poison damage and a -2 penalty to will defense. You don't make separate saving throws against the ongoing poison damage and the will defense penalty; you make a single saving throw each round against the hellish poison itself.
Emphasis mine. You save against the "power" causing the condition, not the condition.
Bad example. That is an example of a power that imposes an effect (poisoned) that imposes two conditions
but specifies that one save ends both. But it is still one effect which is why a single save removes it.
And I agree, it is somewhat sloppy rules writing and should read "you make a single saving throw each round against the effect of the hellish poison itself". In that sentence they are trying to make the point that one save ends both (as an exception to the more general rule of one condition per effect). To interpret the choice of the word 'poison' rather than 'effect' in that sentence as implying 'power' rather than 'effect' is reading too much into it.
But what they
never say (and what you are arguing for) is that you are saving against the
power that imposed the effect rather than the effect itself.
And nothing in there indicates that if two imps poisoned you, you would have to make two saves.
And comparisons to prior editions are misleading and (imho) the source of the confusion. In prior editions, spells did not impose effects. Spells imposed enchantments that
were layered on the target and thus it was logical to speak of multiple instances of a single spell affecting a target and thus perhaps not stacking, but having to be individually removed (or having independantly ending durations).
But that is not how 4E works. There is no enchantment that you can remove. There is no dispel magic to remove the dazed condition. Dazed (or poisoned) is, like damage, something the attack does to you -but once the power has inflicted its effect, it is done. The power does not have a duration.
Powers impose effects.
To put it another way: An effect is what a power imposes. No lack of clarity, just a wide range of possible effects. Some effects are single conditions, some effects are multiple conditions. But the effect is not the same as the power, just as damage is not the same as the sword.
And if you have an effect in place, there is nothing to indicate that a second hit will impose a second instance of the hit (and there are stacking rules to indicate that they won't).
If you are dazed, being hit again makes you.... dazed. (You aren't more dazed and there isn't a spell aura hovering over you to redaze you if you make a save). And when you save (one roll) you will no longer be dazed.
Question: If I am hit multiple times with a power that makes me prone (effect), how many times do I have to rise before I am standing up?
You are either prone, or not prone. You cannot be prone four times over.
You are either dead, or not dead. You cannot be dead four times over.
You are either dazed, or not dazed. You cannot be dazed four times over.
The only cases where there is an issue are:
What if you have identical effects with differing durations? And the book specifies that only the effect with the most time remaining applies (PHB, page 278).
What if you have identical ongoing damage effects? And the book specifies that only the highest value of ongoing damage applies. (PHB, page 278). (Also note - the book specifies that when you have two different types of ongoing damage, you have to save against each of them separately. It does not make that same statement in the section on the same types of ongoing damage).
Bottom Line: The RAW are not 100% clear on this issue, but the preponderance of evidence suggests that effects do not stack and you only need to save once no matter how many attacks attempted to impose a specific effect on you.
Carl