I've been reading up on Familiars in general and the Summoned Stones in particular, as I am playing through the first Quest of the Kindred Fire campaign with a Geomancer.

With the info being fragmented (core rulebook, FAQ official and unofficial, Lair of the Wyrm rules, online threads), I'm trying to wrap my head around the Summoned Stones as Targets.
Because Summoned Stones sit somewhere between the two "normal" types of Familiars (those treated as Heroes and those not treated as Heroes), it's a bit harder even.

However, and this is just more as a "What are other players' thoughts?" than an open question, if I strictly adhere to the most relevant texts , I do arrive at a conclusion.
The most relevant texts (with my emphasis):

• The Summoned Stone card reads: "This familiar is treated as an obstacle , but may be targeted and affected by any attack ..."
  • My interpretation - Not treated as a Hero, expect as the target of an attack .
• Road to Legend rules (Appendix I, Class Skills) read: "Although Summoned Stones are not heroes or treated as hero figures , they are still targeted by monster actions as if they were."
  • My interpretation - Strengthens the premise that these Stones are not heroes or treated as hero figures. However, expands on the attack to include monster actions. Which means, that for instance for monster movement purposes, they are valid targets (with attribute scores of 0, when relevant).

With that preamble, on to my point.

A Monster Activation panel (see Road to Legend rules) includes a Special Effect at the top and the Action / Activation List at the bottom.
In one example, the Special Effect requires each Hero to immediately make a test, which a Summoned Stone would fail automatically.

My conclusion in this case, whether or not Summoned Stones are legal Targets within the context of the strict rules adherence (interpretation) outline above in bullets, is that the Stones are not legal targets for this (or any) Special Effect. Why? Because a Summoned Stone is an obstacle , not (treated as) a hero (figure). And the only exception is when determining targets for monster actions . A Special Effect is not a monster action, even when it triggers off of for example adjacency to monsters.

The only instance where I could see a Special Effect targeting a Stone, is when that Effect includes an Action keyword or symbol, or has the Attack keyword in its text.

My apologies for the long-ish post to come to a point that may be quite evident for some. Thinking through these niggly rules questions, and posting that thought process, helps me ground such rules questions more firmly in my mind. Especially when other players are so kind as to read my post and comment on its contents.

You may find some of this of value:

3. Familiars treated as obstacles

• are not considered to be heroes or figures.
• can be targeted or affected by monster and hero attacks.
• can be affected by conditions, automatically fail attribute tests and may use their action to perform an action printed on a Condition card (e.g. to remove Stunned, Bleeding, and Burning).
• cannot be counted through except for the purposes of being targeted or affected by an attack.
• cannot be moved through.
• may perform a single move action per activation.
• cannot move through blocked spaces (e.g. occupied by enemy figures), except through spaces occupied by friendly figures.
• treat any special terrain that is not an obstacle as a water space, are not affected by hazard/lava at the end of their activation, and can freely move out of a pit space.
• familiars of this type: Summoned Stone

The above applies to Descent in general. There are modifications to these rules for Road To Legend as follows:

• Familiars are not affected by perils.
• When a monster is instructed to target a hero, attackable tokens and familiars treated as heroes or obstacles are included as possible targets.
• For the purpose of targeting, if a familiar or attackable token does not have the statistic the monster is targeting, that familiar or token is considered to have a value of 0 for the corresponding statistic.
• Familiars are removed from the map in between stages of The Delve, except Brightblaze, who is positioned adjacent to Challara when heroes are placed on the map of a new stage.

All of the above information (as well as much, much more) is contained in the CRRG, created by Sadgit with input from FFG, the FAQ, other members of the Community, unofficial FAQ e-mail rulings, etc. This document does a SUPERB job of collating all of the rules from the game across multiple platforms & expansions into a single document. You can find the latest versions of these documents here:

CRRG (Community Rules Reference Guide)

In addition, you can find a lot of valuable information within the stickied thread at the top of the main forum called Index of Useful Links

Thanks for that, I was not aware of the CRRG (I somehow must have missed it in your incredibly useful and actively maintained Index).

I cannot in all that find a definitive answer to the problem I encountered. I will repeat the full text of the Special Effect here:

Quote

Each hero adjacent to 1 or more kobolds immediately tests [Might]; each hero adds 1 [shield] to his results for each adjacent kobold. Each hero who fails is Stunned.

Now it's clear to me that if a Summoned Stone is affected, it would become Stunned because it fails all attribute tests automatically.
Furthermore, if Terracall is exhausted, you can either forego the move or the attack to become unStunned, and do either one of those actions during its activation. (I mention this because it's not explicit in the rules or the official FAQ)

The question is: Does the quoted Special Effect target a Summoned Stone? Per the text you quoted from the CRRG, that is to say the most applicable line:

• "When a monster is instructed to target a hero, attackable tokens and familiars treated as heroes or obstacles are included as possible targets."

My interpretation still stands, in my opinion. Because the Special Effect's text does not imply that the kobolds are "actively" targeting the heroes (which may or may not include a Stone).
The Special Effect's trigger is the state of certain game elements in relation to each other at that moment.
Thematically I would argue that a Summoned Stone won't freak out (or lose its balance, depending on your interpretation of the effect) because a bunch of kobolds are running around it.

Anyone's thoughts on this specific Special Effect and whether or not it targets Summoned Stones?

In Descent "target" usually is a target space or figure within an attack. Out of my head I can't think of an non-attack effect that "targets" a figure. Thus, Summoned Stones are not affected by Special Monster Effects that do not cause monsters to attack.

And you are right that the attack granted by Terracall could be used on actions printed on Condition cards.

Interestingly, accordingly monsters should be able to remove Stun with an attack granted by Frenzy or Flurry. I have not thought about that until now.