Statting accessibility "except when watched" and mechanics thereof?
 

In many different horror settings, creatures often seem to have many times their normal power the second all eyes are off of them. For example, vampires 'wooshing away' either moving many times faster than normal or using some kind of warp, or a strong monster can only bang on blast doors until nobody is observing, then suddenly it can break through in a few hits.

In order to stat this kind of accessibility to a reasonable modifier, I feel like first we need to define when exactly it applies.
Some examples of being watched:

• Engaged in combat with somebody, such that they're closely monitoring your movements both for defensive and offensive reasons. (Unless they're restricted to 'Do Nothing' maneuvers)
• Somebody using Aim or Evaluate against you, even if you're not fighting.
• Somebody using Observation, Body Language, or other skills on you that require close attention.

There should also be ways to "break out" of being watched. If you have a single watcher, something like throwing sand in their face might give you a second or two unobserved. Having some kind of Innate Attack(Wall), Obscure, Mental Illusion, or equivalent mundane countermeasures (running around a corner, a smoke grenade, etc) seems like they should allow breaking the "Watched" status at least in some circumstances.

How would you rule this kind of accessibility, and how would you price it so that players might see it as a different flavor of "Emergencies Only" that easily applies when working alone (or with allies, who would learn not to "Watch" to person with such abilities) but not in the company of opponents, especially not when opponents know of your limitations?

Re: Statting accessibility "except when watched" and mechanics thereof?
 

The first thing I'd do is ask what advantage it's for. Mind reading (except when watched)" is much more restricted than Warp (except when watched) because Mind Reading requires a person to be there. It would require you to see a person who hasn't seen you so how good's your Stealth?

Re: Statting accessibility "except when watched" and mechanics thereof?
 

Check out Ghostly Movement, page 20 of GURPS Horror for 4e, which features Accessibility, Only if Unobserved, -20%. It's a build for Warp for e.g. the way a slasher movie villain vanishes if you don't keep an eye on him, and appears somewhere mildly implausible for an ambush without anyone ever hearing him.

Re: Statting accessibility "except when watched" and mechanics thereof?
 

Typically, such advantages are self-empowering advantages, like movement speed or abilities, significantly greater strength, and other "monster super powers".

Mind reading "except when watched" might not be as big a limitation as it seems, because if you can set up an interrogation-style environment, you just need the mind reader to walk around behind the interrogated while others allies are distracting them. I do, see, though, that different kinds of powers might warrant different limitation values, as is done for some other limitations.
I like that there is a canonical "Only If Unobserved", but I wish it went into fleshing out mechanics for what that means. When player characters have such abilities, or have the option of taking such abilities, the exact details matter more.

Re: Statting accessibility "except when watched" and mechanics thereof?
 

I treated it as no sapient entity is looking at the character.

Re: Statting accessibility "except when watched" and mechanics thereof?
 

The classic example of this is, of course, Invisibility. (c.f. Mystery Men)

Re: Statting accessibility "except when watched" and mechanics thereof?
 

That one was harsher though because it was only useful against cameras.

Re: Statting accessibility "except when watched" and mechanics thereof?
 

I'm sure someone has tried to stat the Weeping Angels before.

Re: Statting accessibility "except when watched" and mechanics thereof?
 

Even then I think it only worked because there wasn't a sentient person observing through the camera, only a simple computer system.

Only if Unobserved -20 and Machines Only -50 and Switchable +10 works out to -60, but the way Invisible Boy had to pause and recite a mantra, probably had some combination of "requires will roll" and "takes extra time" and "preparation required" to bring it to -80.

I can't remember if he removed his clothing or if it just fell to the ground (insubstantiality?) when he turned invisible.

Re: Statting accessibility "except when watched" and mechanics thereof?
 

He had to strip.