So, I thought I'd written my CS query pretty clearly, but it still took several iterations to get a clear answer. On the plus side, they're consistent and really quick - CS didn't used to be
this quick in answering queries

.
So I'd asked if the Centaur Hunter's multi-attack ranged attack would suffer marking penalties if only one of the three targets were the defender.
Jamie (CS) answered:
Yes, if all the attacks made by a marked target do not include the PC that put the mark on them, then the additional attacks would be at -2. Please let me know if you need anymore help!
...which confused me because of the "all" and "additional" words - something got mixed up there, so I asked:
Hi, you answered the specific question concerning the Centaur Hunter's Triple Shot power. I don't quite understand the answer though: you say that "if _all_ the attacks made by a marked target do not include the PC that put the mark on them, then the _additional_ attacks would be at -2" (emphasis mine). I'm not sure which attacks are "all" and which are "additional" here.
Since I asked whether a Centaur Hunter that targets the defender that marked him and two others would take a -2 to attack rolls vs. those two others, I suppose you mean that attack rolls vs. all additional targets (those two others) would take the -2 penalty. That implies those two targets aren't part of the same attack (despite being part of the same power) - but why?
In any case you didn't answer the general question:
"In general, how can I distinguish between attacks that can include several creatures (e.g. a breath weapon) and attacks that consist of separate attacks on several creatures?"
I'd like to understand this because in reading monster stat-blocks, I come across many attack powers that have multiple targets. Some of these count as one attack; others apparently don't - but _why_? How can I tell without asking you for each one?
Jamie (CS) answered:
Any attack that does not include the PC that marked the creature, regardless if they have 1 attack or 3, suffer a -2 to the attack(s) roll(s) if they do not target the PC that marked them. If the attack targets multiple targets, such as a breath weapon, you would get the -2 penalty to attack rolls for any attack that doesn't target the creature that marked you. The key here is in a breath or other type of attack, is to target the PC that marked the creature. Please let me know if you need anymore help!
...which doesn't really address the multi-attack issue at all, but suggests that one "attack" with multiple target is OK but multiple attacks aren't - without saying what the difference is. So, I assumed that something like the Centaur Hunter's triple-shot would be one attack with multiple targets:
Right, so if I understand correctly:
Triple Shot
Ranged 25/50; targets one, two, or three creatures; +19 vs. AC; 1d12+5 damage.
So that's one attack with up to three targets and as long as one of the targets is the PC that marked the Centaur Hunter, the mark is not violated.
(I realize I could have simply asked what an attack is - say whether the target line matters or the ranged/area nature or whatever, but I don't want to bias the answered based on notions we've developed in this thread - so I asked the questions without referring to rule minutiae).
Jamie answered:
Not quite. If you have a single attack that can target 1, 2 or 3 creatures, all the attacks must target the PC that marked you or they suffer the -2 penalty. So in your example, if the Centaur does a Triple shot and the 1st attack targets the PC that marked the centaur and the 2nd and 3rd shots do not target that PC; then the first attack against the PC that marked would not be at -2. However, the 2nd and 3rd shots would suffer the -2 penalty as they are not targeting the PC that marked the Centaur. I hope this clears things up for you.
Now, at this point I'll give the rapid-fire CS queries a rest...
I never mentioned close vs. ranged vs. whatever and how that interacts with marks. I referred to a power that has a ranged attack three targets and tried to present it as reasonable that targeting the defender only once would be "including" the defender. Consistently however, CS thinks this should count as violating the mark.
I'm pretty convinced again at this point that it just doesn't matter how the power is written and whether it refers to other powers or just lists targets inline; inferred RAI by CS is that each individual melee, ranged, close and area attack is considered separately for the purpose of marks - i.e. just as RAW.
That basically means that these kind of artillery&skirmisher creatures can be marked very effectively - if the mark penalty is particularly severe, it may be preferable to not trigger the mark by targeting only the defender although that's generally not going to be the case. Assuming a solo is reasonably made (i.e. has respectable attack/damage), a solo is also encouraged to pound the defender, and that some, particularly MM1, solos aren't enough of a threat - which isn't really anything new. If a defender doesn't break a sweat when faced with a solo focus-firing on him, then that solo just isn't a threat; regardless of marking rules. Note that quite a few solo's just won't care much about the mark penalty - For instance, a paladin's Divine Challenge just looks rather wimpy when put next to most solo's huge number of hitpoints - and it only triggers 1/round.