Pratchett like supernatural ability

[yewrock]

Susan Sto Helit had this ability to make herself completely unnoticeable. It wasn't a disguise and it wasn't invisibility. It was an innate trait that had a concentration check that was nearly impossible to overcome. I don't know if there is a spell or a feat or a magic item that already exists. The best way I can describe this is the subject of the effect is almost instantaneously forgotten and if someone were to try to describe them while looking directly at the subject they would be hard pressed to come up with anything other than medium sized individual.

[aimlessPolymath]

The best way I can think of for simulating this is a modified Stealth check, which is opposed by Concentration(3.5)/Will(Pathfinder or 3.5)/Wisdom(5e) check rather than the normal Perception check.

[Grod_The_Giant]

Mass Cloud Mind is a decent starting point. Given that Susan inherited the ability from a above-divine being like Death, though, I think "pure plot power" is also reasonable.

[Demidos]

Requires a DC 20 wisdom check every round to keep details about their appearance in your mind? That's if you want it to be utterly impossible for anyone to remember it ever. A more sane option might be a DC 10 wisdom check, which means they will likely be forgotten within a minute, but not instantly, and can be remembered by the most powerful.

[BlackLamb]

Susan Sto Helit had this ability to make herself completely unnoticeable. It wasn't a disguise and it wasn't invisibility. It was an innate trait that had a concentration check that was nearly impossible to overcome. I don't know if there is a spell or a feat or a magic item that already exists. The best way I can describe this is the subject of the effect is almost instantaneously forgotten and if someone were to try to describe them while looking directly at the subject they would be hard pressed to come up with anything other than medium sized individual.

I think the Sanctuary spell works like this. If not, I'm sure it could be modified to do so.

[Vogie]

That's an awesome idea. The protagonist from Claire North's A Sudden Appearance of Hope also had that ability, but the other side of the coin - No one who wasn't looking directly at her, or a picture of her, could remember her.

In 5e, I would agree - basing it off of Sanctuary, specifically the uber-sanctuary of the Tranquility & Open Hand monks, would be the best way to frame it.

[Grod_The_Giant]

The Sidereal Exalts from Exalted have a similar ability as well, if you're willing to look at how a different system handles that.

[jqavins]

Susan Sto Helit had HAS this ability to make herself completely unnoticeable.

Susan Lives!

Anyway, this is very similar to Douglas Adams's SEP field, not that this helps in placing it in game terms.

Demidos, I'm not sure but I think I've made a Detect Misunderstanding roll in your response. Susan turns this ability on when she needs it. If you met her when it is not on, you'd remember her just fine. In the unlikely event that you noticed her while it is active, you'd forget what she looked like a moment later, recalling only that you thought you saw somebody, but she (or was it he?) seems to be gone now.

So, how about this? I'm writing it as a supernatural ability, in accordance with the thread title and Susan's nature, but there could just as easily be a spell or magic item that grants the same.

I'm Not Here (SU)

A person using the I'm Not Here ability is very difficult to notice. A person or other being who would otherwise see her must make a DC 20 [spot|perception] check to notice her. After noticing her, he may make a Concentration check, also DC 20, to keep her in sight. Moving more than a five foot step, attacking, or taking virtually any other action raises the Concentration check DC to 30.

A character who has noticed her and subsequently fails a Concentration check (or does not make one at all) will only briefly remember having seen her. A stranger (or passing acquaintance) will remember only having seen someone, and that memory will fade after one round. A person who knows her well will remember having seen her specifically, and that memory will last for two rounds. In either case, he will not remember details such as where exactly she was or what she was doing.

[aimlessPolymath]

To generalize that a bit, I rather like the idea of, rather than a static DC, a modified Stealth check:

Nobody Important (Su): You may make a Disguise check to disguise yourself as nobody in particular. Rather than a Spot check, a Concentration check must be made opposed by your Disguise check in order to see you; those who fail by 5 or less may describe a perception that "someone is in the room", although they cannot identify who or where it is, while those who fail by 6 or more simply do not notice you at all. Once someone notices you, for the next minute they may take a move action to gain a +5 bonus to the check to spot you.

(Inspired slightly by Tumblr stories of DMs asking for highly inappropriate checks: knowledge(religion) to search a corpse, revealing that it's an undead; Diplomacy to talk your way through a locked door, etc.)

[Sicarius Victis]

To generalize that a bit, I rather like the idea of, rather than a static DC, a modified Stealth check:

Nobody Important (Su): You may make a Disguise check to disguise yourself as nobody in particular. Rather than a Spot check, a Concentration check must be made opposed by your Disguise check in order to see you; those who fail by 5 or less may describe a perception that "someone is in the room", although they cannot identify who or where it is, while those who fail by 6 or more simply do not notice you at all. Once someone notices you, for the next minute they may take a move action to gain a +5 bonus to the check to spot you.

(Inspired slightly by Tumblr stories of DMs asking for highly inappropriate checks: knowledge(religion) to search a corpse, revealing that it's an undead; Diplomacy to talk your way through a locked door, etc.)

Working like that, it could also be a Sense Motive check to realize that the person is worth noticing and remembering.