Ok, I'm gonna throw this out there for discussion, in it's own thread. Some of it relates somewhat to an interesting discussion revolving around Fear and surge spending in the "Monsters with Dodge" thread.

Firstly, we must be clear. Stacking and Ranking are different terms used in the rules in different places at different times. They appear to be slightly different, but their effects are more or less the same. Some abilities may both rank and stack (Command clearly has ranks from some sources and equally clearly stacks according to it's description).
It is, I suggest, possible that stacking and ranking are in fact the same thing just with two different names due to the inept rules writing skills displayed by FFG. But that is an aside and not really the point.

Anyway...
Who says some effects (Web, Knockback, Poison etc) explicitly do not stack, just because we haven't been told that they do stack? If it is in any rulebook or FAQ answer then I can't find it (if it is then most of this post is probably void). The question simply hasn't come up. Suppose there was a room/area/level effect that said every attack in that area gained Web. Suppose a Master Banespider attacked in that area. Would the target receive two web tokens? Some would say yes, some would say no. I don't see any clear direction in the rules either way?
(In fact, it could already have come up. A 'natural' poison attack hitting a hero standing on Giant Mushrooms! Has this happened to anyone?)

There is a passage in DJitD which states that some effects will generate no extra benefit if triggered more than once - which kind of implies that they can stack, or be triggered more than once (but is rather offhand while referencing something entirely different). Knockback is explicitly given as the example of this, though that has since clearly changed in expansions with the release of weapons which have knockback and can pay for additional spaces of knockback with surges. It is very clear that Knockback now has a stacking type of effect. It seems to be neither a stack or a rank but to be basically the same thing as additional ranks/stacks of Blast. Basically I'm calling that an effective stack, even if it is not clearly named as such.

Before the RtL rulebook or until someone got an answer to a question from FFG) you would have added Reach to the list of special abilities that presumably did not stack because we hadn't had any opportunity to see them stack yet. But when it does come up, the answer every time (so far) is that the ability in question does stack.

I hypothesise that it would be more accurate (or at least a logical conclusion) to state that all abilities stack/rank in some way unless they are specifically mentioned to not stack. In other words, stackability is the default.
Many simply do not or have not had any opportunity to stack/rank and so were not, at the time of writing the rules, mentioned as abilities that do stack.
Is there any ability that has definitively not stacked? (ok, I found one, Stealth, which is explicit in the rules, so covered already in my statement above).
Others by their nature, find stacking meaningless (eg grapple, fly etc), which does not actually preclude them from stacking, just makes it pointless to explicitly state that they do.

Aura - Ranks, and presumably stacks. Anyone played the Aura mage with the Aura skill and not stacked them? Or the Feat and the mage/skill?
Bash - The description of Bash includes it's own rank/stack system and (with FAQ answers) precludes any other ranking/stacking.
Beserk - Ranks
Black Curse - not explicitly clear but you would expect it to stack based on command.
Blast - Ranks and stacks
Bleed - never seen any opportunity to stack, who knows. Putting 2 bleed markers on from 2 sources of Bleed (say weapon + off hand) is not unreasonable, which would be stacking.
Bolt/Breath - meaningless.
Burn - Ranks and stacks
Command - Ranks and stacks.
Dark Prayer - The description of Dark Prayer includes it's own rank/stack system already. No opportunity yet for further Ranking/stacking. Could easily work like Knockback if it did stack/rank (gain/spend an additional surge for each extra rank/stack)
Daze - stacks
Fear - Ranks and stacks
Flying - meaningless
Frost - no opportunity yet to stack. No reason why a stacked/ranked effect couldn't put two Frost counters on at a time.
Ironskin - meaningless
Knockback - stacks, effectively
Leap - meaningless
Leech - no opportunity yet. Tricky to judge due to it's effect taking multiple counters off rather than adding counters on. Could easily work like Knockback if it did stack/rank (remove 1 additional counter for each extra rank/stack)
Morph - meaningless
Necromancy - meaningless
Pierce - Ranks and stacks
Poison - very rare and hasn't come up yet to my knowledge. Could easily work like Leech/Knockback should it stack.
Quickshot - given the Rage ruling could easily be regarded as stacking/ranking. Otherwise unclear or meaningless.
Reach - Ranks (stacks actually, since the sources so far will always be different and sized 1 each, but described as Ranked - more evidence for the ranking=stacking position)
Regeneration - Ranks
Reinforce - meaningless
Shadowcloak - meaningless
Soar - meaningless
Sorcery - Ranks and stacks
Stun - not sure if it has had an opportunity to stack yet (any gold items do multiple stuns? probably not). No reason why it couldn't stack/rank putting on two tokens from one attack
Swarm - No opportunity yet. Seems meaningless since it basically includes it's own style of stacking internally. However, it could possibly stack/rank should an opportunity arise, adding 2 dice per extra figure (or silver dice)
Sweep - meaningless
Trickster - Ranks
Undying - apparently meaningless. There are actually figures who get undying (of a type) from two different sources in one of the expansion quests. Their own undying (if they have it) from their monster card and a quest specific Undying (on a blank IIRC) from the quest rules. And in the Gold Legendary Dungeon (which is just plain old normal undying). There is no indication in either case (AFAICR, maybe there is) as to how to treat creatures that have undying twice. Maybe it ranks, maybe its meaningless and having the ability twice just means you have the ability twice without increased affect (like Reinforce, Shadowcloak etc)
Unstoppable - meaningless
Web - no opportunity yet. No reason whey a stacked/ranked effect wouldn't put two counters on.
Stealth - explicitly does not stack (possibly because there is only one stealth die!)
Ghost - meaningless
Tread Ice - meaningless
Swallow - meaningless. Could possibly stack allowing additional heroes to be swallowed for each rank/stack (multiple stomachs!)

This is a pretty out there post, and may be completely invalidated by a single line in the Rules that I have repeatedly failed to find. So be it.

I'm fully on board with that reasoning and list. My only addition/change would be to Trickster (and its admittedly nit picking)

Trickster should be listed as Rank and Stacks. I don't think there are any monsters with Trickster 2, but the effect explicitely stacks.

RtL rulebook:

Trickster
The overlord’s cost to play trap cards is reduced by one threat for each rank of Trickster a figure has, while it remains in play. If more than one figure in play has Trickster, the effects are cumulative.

Big Remy said:

Diamond and I believe also Gold master kobolds have Trickster 2 if I'm not mistaken.

The advanced Knockback weapons actually do not grant Knockback twice, as I recall; they grant original effects defined on the card which enhance or replace Knockback . The fact that they felt the need to bother defining new effects on the cards seems to me a strong indication that if they simply wrote Knockback twice (or "~: Knockback ") that it would NOT combine in the way they wanted, and therefore that it doesn't stack, not that it does. There's a similar convention followed with the Stun runes, though in that case they have also rewritten the effect to only work if you inflict wounds, so they would have had to define a new effect even if Stun had ranks.

Your information on Reach is also incorrect--it's entirely possible for one hero to gain Reach from two sources simultaneously using only the WoD expansion (Lord Hawthorne + Walking Stick, for example). I'm not sure what RtL says, but outside of RtL, I'm aware of no indication that this would stack, and I believe it has been suggested that this is another deliberate ability change for RtL, like Undying .

I think if you simply evaluate the abilities as described in the rules, it will naturally result in some of them "stacking" and some of them not. For example, Black Curse says that enemies within 3 spaces get -1 damage/range. So when you make an attack, you check all enemies within 3 spaces for this ability. If you encounter one, you apply -1 damage/range. If you encounter another one, you apply -1 damage/range. The natural result is that it "stacks." But that only works if there are multiple figures with Black Curse --each individual figure either has it or doesn't.

On the other hand, Knockback says that a figure damaged by an attack with Knockback can be moved up to 3 spaces by the attacker. So when an attack occurs, you check whether the attack has Knockback . If it does, the attacker can move the target up to 3 spaces; if not, he can't. In either case, there's nothing left to check after that. Either the attack has Knockback or it doesn't. But it "stacks" in the sense that if you make two attacks that each have Knockback , you get to move the target each time.

Furthermore, the fact that they defined ranks for some abilities that are equivalent to simply having the ability work N times, and that they said that you add ranks when you get a ranked ability from multiple sources, and that they did not do any of that stuff for other abilities, says to me that they thought about stacking and made a conscious decision.

That doesn't preclude them from changing their mind later, of course, as apparently happened with Reach and Trickster , at least in RtL. And it does look as if they decided to make "doesn't have ranks" the default for any ability where it didn't matter in the expansion where it was introduced, which was probably a poor choice from a design standpoint. As I've mentioned before, I'm doing a rewrite, and in my rewrite, lots more abilities have ranks.

But I think your claim here is ambiguous (not sure how you categorized Dark Prayer, for example), and I don't see any particular support for it in the rules.

I'm not an expert, but the way I see it in the rules is that only special abilities with ranks have their effect stacking. So if a Special ability has never been seen on a card with a number next to it, it means that the effect doesn't stack, unless stated in the description of the ability. Like "Trickster" in WOD.

P.22 (JITD): "Some special abilities have ranks (e.g. Fear 2 or Blast 1). The effects of these ransk are always explained in the ability description. If a hero or monster gains a given special ability from more than one source, any ranks the ability has are added together."

What is the example for Burn having ranks?

Aura: ex: Shiver

Berserk: ex: Blood Apes in RLT.

Command. Ex: Master Beastmen in RTL.

Pierce. Many examples like skeletons.

Fear. Ex.: Dragons.

Blast. Ex:: Lava Beetles.

Regeneration. Ex: Sir Alric Farrow?

Trickster. Master Kobolds in RTL.

Ok, rethinking time, in light of additional research.

Ranks and stacking are different.

1. Ranks are specific effects which in all cases have the explanation of what happens for multiple ranks as part of the ability explanation.
DJitD pg22
The effects of these ranks are always explained in the ability description.

2. Stacking, in every example we have, is a purely additive effect.
DJitD pg 22
If there are multiple figures with Command within three spaces of a figure, the effects stack (e.g., the figure would add 2 to the damage and range of its attacks if two figures with the Command ability were within three spaces of it).
FAQ pg 6
A: Special abilities that require you to spend surges are designed to stack. So if you have an ability such as “?: +1 Damage and Pierce 1,” and you pay 3 surges, you gain +3 Damage and Pierce 3.

3. Ranks explicitly add together (basically stacking but in the way explicitly mentioned in their own explanation) for any hero or monster who receives the ranks from more than one source.
DJitD pg22
If a hero or monster gains a given special ability from more than one source, any ranks the ability has are added together

The question is what happens to effects that are affecting a monster or hero but are not 'received' by that monster or hero?
Examples would be Fear (which sparked this). Fear is not received by a hero or monster (at least not when operating) but instead affects him/her/it.
Black Curse is another example. If there are two sources of Black Curses within range of a hero or monster, do they add? The hero or monster is not 'receiving' the Black Curse ability, he is being affected by it.
Arguably Command is another example (though it is explicit how it is treated). A hero/monster within Range of two sources of Command does not 'receive' Command himself, he is instead affected by Command.

I believe we have enough evidence, between Command, Trickster and Ranks stacking when a hero or monster receives them from more than 1 source, to consider that ranks always stack (each in their own way). This is in fact simpler than saying everything stacks, in various ways, as it gets around those things that don't have ranks and/or would find ranks/stacking meaningless.
But it would be reasonable to request a clarification to this effect (or not) in the next list of questions which go to FFG. Anyone disagree?

PS The Burn example was misremembered from the Gold item with Blast 2 and Burn. I thought it was Burn 2 and Blast.

So is it now your contention that unranked abilities never stack? That would seem to contradict your earlier feelings on Black Curse, and runs into potential problems when you consider that Command explicitly stacked back when it didn't have ranks.

By the way, another bit of research for you: the surge-spending example on page 10 of JitD specifically states that spending surges to gain Knockback twice on the same attack would produce no additional effect.

Antistone said:

Look, I'm just trying to get something ordered out of a mess. I botched it the first time (which happens) because I missed a couple of critical rule notations. I do recall noting it was an 'out there' post, basically thinking out loud to try and get more minds than just one working on it.

I know the Knockback example was used originally. That's part of the whole reason I'm trying to get something ordered. First we have knockback not adding anything, then in a later edition we have Knockback with ranks that can add (sometimes). Similarly, first we have Reach apparently not ranking despite an ability to get it from two sources (I mistakenly thought the sources were from different expansions), then we have Reach ranking after no other changes.

What happens then, is that each ability, is uniquely defined with no pattern. Every time an expansion comes out that ability may be uniquely redefined. Which is ok, until you get interactions that haven't been uniquely defined. If we could get some sort of definition going that we could propose to FFG then we could have a guide as to how to apply interactions that haven't been defined yet.

None of that changes the three statements, and conclusions, made in the last post on this thread. It would be a lot more useful if you would address them instead.