[johndallman]

Obscure [2/level] is an exotic physical advantage. You can produce some kind of effect that “jams” a human sense, or a sensory advantage, giving people using that sense ‑1 per level of your Obscure to detect you. This advantage appeared at GURPS 4e, as a generalisation of the 3e advantage Smoke.

Examples of Obscure include fog, radar jamming, and white noise for vision, radar and sound respectively. Ten levels of Obscure will block the affected sense entirely. By default, Obscure affects a two-yard radius, centred on you, but this can be modified with the Area Effect enhancement. By default, the boundaries of this area are easily detected with the affected sense (+1/level to Sense rolls).

Special modifiers for Obscure include Always On, ‑50%; Defensive, so that your own senses are not affected, +50%; Extended, +20% per extra sense affected; Ranged, +50%, which allows you to place the effect as a ranged attack (unlike most ranged powers, you can use it again before the duration expires and it thus costs more) and Stealthy, +100%, which makes the effect “invisible” and removes the bonus to detect the boundaries of the effect.

Ten levels of Obscure (Vision) with Stealthy costs the same as Invisibility, but doesn’t give the same effect. With Obscure, witnesses can’t see through you, so there’s clearly something going on; with Invisibility, there are no such clues. Obscure with Stealthy works better with senses that don’t form images.

Powers adds considerable detail, about types of senses, effects on Telecommunication that uses the same means as the obscured sense(s), stealth fields, weapons and other ranged attacks, and boundaries with other traits. It adds Limited, ‑20% or ‑40%, which limit its effects to a power source, or a specific power.

Obscure is used to model natural abilities like a squid’s ink glands, or skunk spray, as well as many kinds of equipment. It isn’t widely used in GURPS supplements, but Martial Arts suggests it as a chi power, and Monster Hunters Power-Ups 1 uses it to affect memories. Power-Ups 1: Imbuements provides ways to use this advantage via weapons, and PU5: Impulse Buys provides a way to make it permanent. Hippos can do Obscure with mud in Powers: Totems and Nature Spirits, and Psionic Powers reminds us that Obscure can make it harder to hit you, provides Anti-Targeting, ‑20%, which doesn’t make you harder to see, just harder to hit, plus a version that does provide Invisibility. Thaumatology: Chinese Elemental Powers uses Obscure for Power Blocks, and Thaumatology: Sorcery uses Obscure (Information Spells).

I don’t think I’ve ever used Obscure, as a GM or a player. I’ve used Chameleon, Invisibility and Silence as concealment powers, but never this one. Have you?