There's been a lot of discussion lately in Eclipse's Rules Forum about invisibility and powers that counter invisibility. This is a very complicated topic in LARPing; we spent the better part of a year (off and on) discussing it while designing DtD, and I'm going to try to summarize the whole topic and various proposed solutions over the course of this post. As a disclaimer, I play one of the most frequent stealth users in Eclipse, in a build path that can never have True Sight. Also, I want it to be clear that I'm not trying to persuade Eclipse to adopt DtD's rules model - I'm just laying out the situation because I think it's an interesting and thorny area of design.
A Bit of History: Invisibility
For readers who don't already know all of this, let's start with the basics. Shattered Isles, King's Gate, Eclipse, and Dust to Dust have all had invisibility mechanics, and the exact mechanics of invisibility have seen extremely little change since their inception in SI. The player receives or activates the effect, which is always a per-day usage (either fixed per-day usage or mana-based expenditure), and places her palms together over her head. As long as the player maintains both that gesture and Concentration, the player is invisible to all other players (except as described in Detection, below). As with all Concentration, the player cannot run, and basically any harmful incoming effect disrupts Concentration, aside from a short list of defenses (that distinctly do not include common defenses like Parry, Dodge, armor, or Skins).
About the Gesture
There is some significant genius in particular posture used for Invisibility - palms together and overhead, which until Eclipse was always empty-hands-only (with the further caveat that claws, available exclusively to NPCs prior to Eclipse, counted as empty hands, as did spell packets). Firstly, it is obvious at some distance, in low light or in silhouette, or from behind. This is useful for recognizing quickly that one should not react to the invisible character, even from across a field.
Incidentally, DtD's rules for invisibility do not allow weapons except for Claws or weapons enchanted with the Concealment enchantment.
Secondly, the gesture is tiring to maintain. My personal record is something like forty-five minutes (no weapons) uninterrupted, and very slightly more (with weapons) for a circumstance in which I got one brief break from a Hold. This is a good thing within the rules, as far as I'm concerned, as it gives the effect an inherent duration limit; I am perhaps lacking in sympathy for NPCs who want to change to a more comfortable gesture so that they can be invisible for hours at a time, since that option is not open to players and loses the other benefits of the normal gesture. It also pushes stealthers away from heavy armor, incidentally.
Thirdly, because dropping out of the gesture ends the invisibility, invisible characters cannot open doors, draw things out of pouches, disarm traps, or do much of anything but walk, sit, or stand. This is a critical limitation, and one of the best defenses against an invisible character within these rules is to enter a building you know they are not currently inside (and don't let anyone else in that the stealther might follow).
A Bit of History: Detection
There is no single invisibility-detection effect I can describe here, since this area of the rules has undergone a great deal of change and redesign since its introduction.
I think it was somewhere during the second Shattered Isles campaign that the first player-available invisibility-detection effect was introduced into the campaign. Tremorsense was a super-secret effect, found in a Double Secret portion of the Stone bond, though once purchased it was always active. I don't believe anyone gained this ability in the entirety of Shattered Isles. Further, we didn't particularly notice its lack, since as mentioned above, all invisibility required empty hands at this stage, and Forestblend (invisibility that had to stay near large trees) was the only commonly-used invisibility effect. SI's Tremorsense was an always-on effect, and if it had a range limit, I don't know about it.
It was relatively late in the second King's Gate campaign before SI-style Tremorsense was admitted to the rules. The second KG campaign had far higher-point characters than the second SI campaign, as well as a much larger population of Stone bonders; one player had the ability almost immediately after it became available. The King's Gate campaign had a much broader usage of free-roaming invisible assassins; I'm pretty sure there was a secret order of Air bonded assassins, as well as the various powers of the Skiazo. While I was not privy to the conversations that resulted from the sudden shift in the balance of power, I am aware that they led to a change in the rules shortly thereafter. I'm not exactly clear on what the new rule was.
Eclipse's detection effect is True Sight, which from the beginning of the campaign was an always-active unlimited-range power. From my possibly-flawed understanding, it requires the user to inform invisible characters that they have been spotted by announcing, "True Sight." The announcement informs the invisible people that they done been made, and the person detecting them is actually making eye contact, rather than accidentally failing to avoid making eye contact. This ruling is unpopular with players with access to the ability who want to lure the stealthed character in by pretending that they do not see them, only to reveal their ruse once the stealthed character is well and truly fucked. Importantly, True Sight is available to two power sets, one of which is very popular (but also limited in its use to nighttime, unless granted an exception by way of a magic item).
As a card to trump PC stealth detection, Eclipse has introduced NPC-only Phasing abilities. Two PCs can stop enemies from Phasing Out, but as of current writing, no PC can sense Phased Out characters or force them back into phase once they are Phased Out. Importantly, the gesture for Phased Out is exactly identical to the gesture for Out Of Play.
Below the cut: a recap of DtD's design debates on detection abilities, including the specific problems with the whole deal that we set out to address.
Invisible NPCs, regardless of the NPC's reason for being stealthed, are frustrating to PCs, because if you can't detect invisibility, there's nothing you can do, and you might well be giving lots of information away to spies.
If detection is always-on and unlimited-range, the invisible opponent is fucked from the start, because a stealthed character has no means of evading pursuit while maintaining stealth. One detecting PC is completely immune to all forms of enemy stealth, and because almost any successful attack ends stealth, that PC's immunity functionally extends to every ally on the field. (Some characters with detection in Eclipse do not carry ranged weapons; with all due respect, I believe this is a tactical error on their part.)
If detection is not unlimited-range, how do you measure range on-the-fly in an action-based situation? LARPs don't handle fixed ranges well at all, as every argument over whether or not someone is in range of a Point effect demonstrates (incidentally, this is why DtD has no Point effects). Some of those involved in the conversation have proposed a range limit of 5, 10, or 20 feet. This has a couple of problems beyond the measurement issue, though.
Let's say you're a player who wants to avoid being cheesy. What is it okay to do when you are aware OOC of an invisible character in the area? If there are range limits on detection, aren't you being cheesy if you let anything but an unrelated external impetus (and how do we judge that?) drag you into the area of the invisible character?
This problem is one of several that has led some people to propose what I'll describe as the Spidey Sense Tingling idea. You get a general awareness that something is rotten in the state of Denmark, usually with a general "somewhere over there" inclusion. This lets you either activate a power that pinpoints the target, or lets you work on getting within range, or something. From a conversation earlier today related to Eclipse's rules:
dude: It would limit true sight more in relation to invis, but still allow it to be always on.
me: so the weird thing that that does is that it means that even if you don't yet know where the invisible character is (technically, IC) you need to act as if you do, so that you'll know when your True Senses can sense them.
dude: Hrm... I'm not looking at it as a 'get into 10 foot range so you can hit them', I'm looking at it as 'invisibility is always perfect unless you're within 10 feet.'
dude: There's no more metagaming available there than there is in the current system, at elast.
dude: Or what if True vision required 3 seconds of focused attention to get a clear view of what was invisible. Maybe you could see that something was moving around in a general area, but you had to get all squinty-eyed to be able to actually point it out.
me: So the idea here is that True Vision gameplay goes basically as follows: True Vision tells you there's someone generally in the area. You don't pinpoint them, though, because you want them to come within weapon range. Once you think they're about within weapon range, you pinpoint them and shoot them, and they have the three seconds of pinpointing time to get out of weapon range. But the guy with True Vision can't approach the stealthed guy, because that's pretty much pinpointing.
me: that last part is important because the stealthed guy isn't allowed to move quickly.
Now, a version Spidey Sense Tingling is at the core of DtD's detection rules, so I don't dislike it per se; my problems with it have everything to do with its details of implementation.
Always-active stealth detection is, for my money, a Big Problem, since it is pitted against a per-day ability (total uses of invisibility effects available per day in Eclipse vary widely, but all are per-day usage). Having spent nothing to detect and reveal the invisible character, the detecting character will be able to do so again, indefinitely. Even when knocked out of stealth, using another invisibility effect to flee will just get me run down and killed.
Quick war story (because it was one of my proudest moments as a ninja cyborg assassin): Having been spotted by the one guy in the pack who had stealth, he rushed up to reveal me. I Parried his attack, breaking my invisibility, cut him to ribbons, killing-blowed him, and went invisible again before his four allies could land a hit. To drive home my earlier point, this worked solely because he only had melee weapons.
If detection is not always-active, what are its limits - in duration, uses per day, or the like? As with the problem of range limitation, under what circumstances do you use this power if you want to avoid being cheesy? If there isn't a "Spidey Sense Tingles" component in the rules, it's much harder to point to an answer to this question.
DtD's answer, after extensive discussion, was to put three different range-unlimited, duration-limited Spidey Sense effects into the game: Sense Hidden (available to Spider Lords, of course!), Sense Lesser Illusion, and Sense Illusion. All three of these Sensing effects have kind of odd durations, as a solution to the problems posed above.
The character casts these spells immediately after mana refreshes. (In the case of using scrolls... kinda whenever. It's trickier because it's a consumable item.)
They remain dormant until a character hidden by a relevant illusion enters the player's field of view.
This triggers the Spidey Sense, which lasts for the next fifteen minutes.
The detecting character can decline to have the Spidey Sense activate if the invisible character is an ally. In that case, they cannot later decide that the hidden character is no longer an ally, at least until some future casting of the same effect. (This was done so that having invisibility-using allies didn't ruin the game for the detecting character.)
If the detecting character chooses to allow the Spidey Sense to fully activate, the player may spend a minute of concentration to gain more information.
In the case of Sense Hidden (nominally the weakest of the three), the user gains approximate number and general direction of invisible characters.
In the case of Sense Lesser Illusion, the user pinpoints one thing concealed by Lesser Illusions (Melds, some personal buffs).
In the case of Sense Illusion, the user pinpoints one thing concealed by Lesser or Greater Illusions (all Meld or Invisibility effects).
Pinpointed characters may be forced out of invisibility with an attack, or with a Dispel Illusion effect (or Dispel Lesser Illusion, for Melds). Since attacks are free while Dispels are expensive, I'll point out that this also works on people you don't wish to attack, people under a Form effect, and illusions on objects that may not be disrupted by attack.
At the end of fifteen minutes, the now-active effect ends completely, and the player is justified in casting the initial enchantment again. Lather, rinse, repeat.
The minute of concentration necessary to pinpoint targets gives the invisible character considerable time to evaluate and possibly change his plans, or to move in on the concentrating character or other opponent to launch his attack. In essence, it forces his hand, but because he may have moved out of line of sight of the concentrating character in the intervening minute, he may still get away clean or get to make a surprise attack.
DtD's rules for stealth detection are some of the most complicated rules in the game that the player needs to remember without a built-in rulebook lookup (cf. ritualism's pervasive and inherent rulebook lookups). This exploration of the problems involved in stealth-detection rules should go some distance toward explaining why we felt we had to do it this way. They haven't seen extensive use in-play yet, so it remains to be seen whether players will handle them comfortably once they're using those powers frequently and in high-tension situations.
Though this post is not primarily intended to offer a proposal for Eclipse's current discussion, I'll end on that note anyway: I'd like to see True Sight work like Sense Illusion (one-minute concentration time to pinpoint one invisible target), except that it simply "goes back to sleep" at the end of fifteen minutes. A more advanced version of the ability might provide an exception to this with a certain number of instantaneous detections per day (but the character can always fall back on the one-minute version when these are exhausted).