Background:
Yes, there are still issues in this, sorry!
Mahkra's post best covered many of them, even though related directly to an 'entering impassable terrain' argument. So here it is;
<Mahkra>I thought the original rules seemed pretty clear, at least in the vanilla expansions, though there's never been a defined general "Movement Sequence" like the Attack Sequence in the JitD rules. We were just given specific instruction for each new type of space. We were usually even given specific instruction regarding large monsters.
(Parts relevant to large monsters in bold below.)
Rubble: "blocks both figure movement and line of sight."
Pit: "if a hero or monster moves so that the figure is only occupying pit spaces, the figure falls into the pit."
Mud: "a small figure must spend 2 movement points ... to move onto a mud space" ... " large figures are affected by mud, but only if they make a move that results in the entire figure occupying mud spaces."
Dart Fields: "each time a hero or monster moves so that any part of the figure is occupying a dart field space, it risks being hit by a dart."
Fog: "Figures have line of sight into adjacent fog spaces. A figure in a fog space has line of sight to all adjacent spaces, but not to any other spaces."
Tree: "It costs two movement points to enter a tree space. A figure in a tree space is considered to have the Shadowcloak ability. l arge monsters only need to occupy one tree space to benefit from this ability. "

Though we're never given a Movement Sequence, I imagine moving to an adjacent space actually involves the following steps:
1. Determine whether the intended adjacent space can be legally occupied. (e.g. not Rubble)
2. Determine the cost (generally MP cost) to move to the intended space.
3. If sufficient MP to pay the cost, move figure to adjacent space, paying MP cost.
4. Suffer any immediate effects of occupation. (e.g. damage from lava)
5. Suffer any prolonged effects as long as that space is occupied. (e.g. restricted LoS in Pit or Fog, Shadowcloak in Tree)

Then came the FAQ ruling:
When large monsters move, they can sometimes find themselves moving across hazardous terrain (lava, scything blades) twice as often as
other figures. Further, it can often be confusing whether or not beneficial terrain (trees, elevated terrain) should affect a creature
only partly standing on it. Use the following guidelines to arbitrate these instances.
The overlord may choose to have a monster affected by any terrain it partially occupies. A monster MUST be affected by any terrain it
completely occupies. If the monster is completely occupying multiple terrains, the figure has to be affected by one of the terrains
(Overlord's choice).

This FAQ ruling superficially seems rather simple, and it does negate one rules loophole for the OL:
* If a large monster is half in mud and half in lava, it now must be affected by one of the two, instead of being able to use each to be
safe from the other.

However, it also raises numerous questions, some of which have been discussed in other places and remain ambiguous:
* When does the OL choose? How long does that choice last? When, if ever, can he change his decision?
* Must the overlord choose to have a monster affected by any single terrain, or could he choose to consider a monster in a tree and on a throne?
* What is considered "terrain"? That term is used in a few places in the FAQ but is never defined. And it's not really used in the rule books. (It's mentioned in component descriptions for RtL/ToI/SoB - map tiles have "dungeon terrain" or "outdoor terrain" - but it's only used in the actual rules once, in the "Rope" part of the SoB rules, and it is never defined. I'd guess that Lava and Mud are probably terrain, at least thematically, but is Fog? Dart Fields? Pits? Rubble?)
* As written, the OL only has a choice about the terrains currently occupied, which means the OL cannot choose to ignore the added cost to move its front half onto a mud space or a tree. I imagine the rule is intended to function the way the rules were written in the WoD and ToI rules, though, and the OL should be able to choose to ignore terrain that the figure does not already occupy but will occupy after movement.

Assuming we can get past those issues, I'm still not sure what the FAQ means by "may choose to have a monster affected by any terrain". This
could plausibly mean a few different things.
A. The OL may choose to ignore occupation effects, such as Fog / Lava / Tree, but must still pay applicable entry costs per the normal rules. (# 4, 5 are conditional in the Sequence above.)
B. The OL may choose to ignore entry costs and occupation effects, but still may not move onto any space that could not be legally occupied by a small figure. (# 2, 4, 5 are conditional.)
C. The OL may choose to ignore ALL effects of a certain terrain, as long as the movement does not result in the entire base being in that terrain type. (# 1, 2, 4, 5 are conditional.)
D. (Something else I haven't considered?)

I believe "B" is Corbon's interpretation. "C" would allow large monsters to occupy rubble and water. But the right answer might also be "A"; I'm not sure why to believe any one of these options is more valid than any other.</Mahkra>

So, it really does seem that the large monsters + terrain needs rewriting right from scratch.

Suggestion:
Replace the Large monster movement section (at least the rules portion) with...
When a large monster moves, several things happen:
* it enters one or more new spaces that it did not previously occupy. When this happens it may choose to count one and only one of the newly entered spaces as 'the' space it is entering. The large monster is then treated as if only moving into that space for the purposes of effects that are triggered when entering a space (eg Mud, Lava, Aura).
* it occupies multiple spaces. At all times, every space that a large monster occupies must be a space that it could legally enter if it was a small monster. <OR replace last sentence with "A large monster may occupy impassable spaces as long as it is not occupying impassable spaces with all of its spaces">
* it occupies multiple spaces. A large monster may claim a beneficial effect from any terrain (obstacle or other prop) space it occupies (eg if one space is in a tree the entire monster has shadowcloak).
<OPTIONAL ADDITION>
* it occupies multiple spaces. When a large monster makes an attack it may choose one and only one space that it occupies to make that attack from. For the purposes of LOS, adjacency, range to target space, Template placement and terrain (obstacles and other props) the attack comes only from that space. For all other affects (eg Command, spaces affected by an AoE attack) the monster may count any and all spaces it occupies for each affect.

Notes For FFG:
The first * covers moving into multiple new terrain types and I think has the same net effect as the current rules.
The second * covers the question on impassable terrain - one way or the other.
The third * covers beneficial effects. Now there is no question of choosing etc.A monster may move into a tree without paying the cost using the first *, then later claim the benefit using this third *. I believe this is how the current wording acts.
The fourth * is an entirely new rule that might be beneficial and might not. FFG can decide. (Or we can drop it before we send to FFG. I personally favour it because it tidies up some small inconsistencies in general play - like hitting with a melee attack from an elevated position even though the target is not adjacent to the elevation for example).

Notes for forum commentators:
Possible issue with the first * - Alertness (and similar). Not quite sure how to get around that yet... Please give ideas!

I really hope someone from the FFG staff reads this, and understands everything. I would hate for someone to just brush by this and not pay close attention to the issues here.

Jonny WS said:

The purpose of this subforum is to get these threads ready to a state that we (a small group tasked with interacting with FFG over the next FAQ will take to FFG.

Last time Big Remy (and Thundercles IIRC) did this task for the most part.

I wasn't involved then, but my understanding is that we will collate these threads back into a document that we will then have joint access to with the FFG staff member, and (s)he can give/choose answers etc. There will be a week or more at least of back and forth, but the document should get reasonable scrutiny from the FFG personnel involved. They will be expected to scrutinise and answer each question (even if just to say 'no answer sorry').

That is why we aim to have the 'background' section before most questions. This means that the FFG staff has all the relevant research and issues laid out saving them the work normally required to get a good understanding of an issue.

What we really want to see here is people trying to improve the initial posts - either by catching mistakes, refining wording, adding clarification or pointing out other potential answers etc.
I don't believe for a moment that all te initial posts are 'good enough' (or 'as good as they could be') to take to FFG already.

Just to clarify: it looks to me like the current FAQ says that the overlord can choose any space that a large figure occupies after the movement to be affected by; Corbon's suggestion involves limiting the choices to squares that the monster entered on that movement, which is significantly more restrictive (but more similar to the previous FAQ change with the confusing "front half" language, or at least what we took it to probably be intended to mean at the time).

Corbon's version (limiting the choice to entered spaces) potentially opens up loopholes where a monster can avoid ill effects by moving in weird patterns that it would be forced to suffer moving "straight". For example, suppose a hellhound is approaching some lava, and wants to move to partially overlap it. If it moves forward in a straight line, the only space it "enters" on its last step is the lava space, so it's forced to take damage. But if it moves diagonally left and then right during it's approach, then it's final step "enters" both the lava space and the empty space in front of it, allowing it to avoid the damage even though it moved to exactly the same position. That's pretty bizarre (especially when you consider that this maneuver is possible only if there's empty space to one side during the hellhound's approach - why on earth should that matter?). You can get even weirder situations involving monsters jumping (and therefore entering many spaces at once when they "land").

Either way, if we go with any variation of the "choose one space" logic, we should think very carefully about whether to extend the rule to apply to abilities as well as terrain. I like consistency, but if we extend it to Aura as Corbon suggests, then, for example, ogres will be able to move adjacent to heroes with Aura without ever being affected by it (but only sometimes, depending on the circumstances); any large monster will almost always be able to avoid Aura damage for failing to move during its activation (since it will just need 1 square that isn't in an Aura). Aura's already a pretty weak effect, it would be sad to see it further neutered.

There's also a major hole in the current rules/Corbon's proposal that hasn't been touched upon: it only addresses negative effects that occur instantaneously when entering terrain, not ongoing effects or effects that trigger when leaving. When, if ever, does a large monster pay extra movement for leaving a pit? Is its line of sight ever restricted for being in a pit? It would be weird for a large monster to count as entering a pit (to avoid some other effect) but then count as leaving from some other space to avoid paying extra movement; but if the cost for leaving is dependent on the terrain choice made when entering, that means that players need to track that choice somehow - potentially across multiple rounds if the monster doesn't move for a while.

(Actually, it's pretty bizarre to think about a monster falling into a pit smaller than its base at all , but that's a separate issue.)

And if we extend the rule to cover abilities, when would a large monster count as grappled?

The stated reason for changing the rules was that "When large monsters move, they can sometimes find themselves moving across hazardous terrain (lava, scything blades) twice as often as other figures," which betrays a misunderstanding of the original rules (lava never worked that way), so I think the motivations for changing these rules in the first place need to be re-examined.

Do people really feel strongly that large monsters shouldn't suffer extra damage when walking through scything blades and dart fields? It doesn't come up that often, and it seems thematically appropriate that they should.

Every terrain effect falls into one of two categories: either it applies when a figure occupies at least one square of that terrain, or it applies only when every square a figure occupies contains that terrain. Impassable terrain, as well as scything blade and dart fields, were in the first category, while pits, mud, lava, and ice were in the second. (You could also understand various abilities such as Aura, Grapple, Command, Black Curse, etc. as falling into the first category, further reducing the number of special cases needed in the rules.)

That leads to thematic weirdness in a few special cases (such as an ogre that occupies one square each of pit, mud, lava, and ice, but isn't affected by any of them), but it's very easy to understand and apply, and it means less errata in the rulebook. A few terrain effects would need to be ruled into one category or the other, but that's not hard.

And I guess you could add a third category for attack-related effects that apply only when you choose that space as the origin for the attack, if you wanted. (Similar to Corbon's fourth *) While you're at it, you might want to get a ruling on whether a large monster is allowed to trace line-of-sight through a square it occupies that isn't the origin square of the attack.

Antistone said:

I agree with this ruling. I would also add a touch to prevent the case of the ogger:

<<Terrain effects falls into one of Whentwo categories: either it applies when a figure occupies at least one square of that terrain (category 1), or it applies only when every square a figure occupies contains that terrain (category 2). When a large monster enters a group of spaces that contain terrain from both categories, only those of category one apply. When a large monster entres a group of spaces that consist only of category-2 spaces, then the monster must choose one among those spaces ("I'm steping on this space") and pay the corresponding penalties of that space only (if any).>>

For now, only mud, pits, lava, ice and empty spaces belong to category 2. It could be argued that corrupted terrain belongs to it too, but since it doesn't affect mosnters, it doesn't matter. I would also add that the pit cannot be chosen as the steping space unless the group of spaces contains nothing else, because the monster "wouldn't fit" inside. This is important when trying to escape from a boulder.

So:

Does the monster enter any spaces of category 1? -> It is affected by those spaces only.
| No Yes
V
Is the monster completely in a pit? -> It is affected by the pit (it is considered to be in or to fall into it).
| No Yes
V
The mosnter choses one of the remaining spaces and is affected by it as if it had just entered it (even if it is the same as the one it was affected in the previous move).

Can somebody reword this as a more presentable question and answer?

Galvancito1 said:

No. You specifically and emphatically should NOT add a rule like that, because it sounds simple and logical until you realize that not all terrain rules are instantaneous effects that apply when you enter, and this becomes horribly complicated and broken when you're also dealing with effects that occur while you occupy terrain or when you leave.

Yes, it's weird none of an ogre's spaces are normal but it still isn't affected by any of the terrain, but that's an extremely rare situation, and if you really care about theme it can be explained away by saying that there's just not enough mud in one square to affect a creature of an ogre's mass, or something like that. It is definitely NOT worth adding in the extra three paragraphs of rules and additional record-keeping that would be necessary to make that "choose one space" rule actually work.

About the previous post of antistone of trace line of sight from a square that is not the origin of the attack when i asked a question like that corbin answered that it is a loophole and that it is indeed possible. The question in specific was about an ogre with reach attacking someone 2 squares away but 3 squares away from the square that he has LOS to that figure. I wonder how other people are dealing with that.

Antistone said:

Please try to follow this reasoning:

Categoty 2 only contains lava, mud, ice and pits.

Pits can only be chosen when there are no other options, so any effect they have on the figure would be applied just as you said (when the monster is completely inside).

Mud and Ice only have any effect when the figure enters it. No effect is triggered by a figure leaving or staying on mud or ice. So no problem either.

Finally, lava does have an effect for figures that stay on it for a whole round and don't move. This effect would be remainded every round, and the monster would rarely choose to finish its move "steping on" lava when there is any other choice. That's of course unless the monster is acting like a kamikaze and probably wouldn't survive long enought for it giving trouble. Beside, just as you say, it is very rare to find lava next to ice and even more rare to mud.

So what exactly is the problem?

The kind of obstacles you mention (whose effects are more complicate than just "do this when you enter it") are those that affect the monster even if only part of it is inside (like trees, mushrooms or elevated terrain). Fog could be a special case, but fog only alters the line of sight. It doesn't matter how big or small the figure is.