This isn't disguise per se....
the character/monster/creature in question has an ongoing magical effect: it's like amnesia to anyone who sees his face. He's so utterly innocuous you can't remember a thing about his face no matter how hard you try.
Later, if asked, you could say (if he's human....I haven't decided THAT yet) "he's human....I know that. I.....saw his face, but.....no, I don't know what color his hair/eyes/skin were. I don't know what his nose was shaped like. I don't know if he had any distinguishing tattoos, or wore an earring. I don't know what he wore. But he was human. Male. It's the weirdest thing."
He's not invisible per the rules. He's not disguised, alter selfed, or polymorphed per the rules.
He's just got a forgettable face.
He is what he is, you just can't freakin remember what that is.
How would you quantify that per 3.5 rules?

I believe that would be using hiding in a mob combined with a hide in plain sight type ability?

You could probably also call it an effective use of alter self or some such, you alter your face to look like one of those police blurs but not so noticible as to be called on it.

Yeah; that helps.
I guess it'd help if I knew what I wanted...

You could base it off of modify memory.

Yeah; that's the closest to what I want.

Maybe something of an antipathy effect, maybe from a magic hat or cloak or something that forces characters to will save just to look the character in the eye or be forced to look no higher than the chest or something like that...

A very interesting concept, thank you. I may just use this myself...

pbp spoiler

Well, I surpose if you want to look at effect rather than fluff, you would get a more concise answer.

Will your pc's be able to target faceless?

If no , invisibility may be your best best

If yes, and you just want them to be unable to get information after the face then a contingent type modify memory would probably work (trigger you look at my face, effect modify memory, forget his face )or some such.

This reminds me of that Jhereg in the Vlad Taltos books by Steven Z Brust who no one ever notices. He's not being stealthy, he's not invisible, he's just not that noticeable. He could be in the room with you, but he just doesn't have any presence. They even mentioned he had to join the Jheregs because back when he was with his old House, he would lead people into battle, but they would lose track of him, or forget he was there, and his forces would disintegrate.

Somewhat similar effect to the Oblivion Item: the Gray Cowl.

...Whosoever wears it shall be lost in the shadows. His true nature shall be unknown to all who meet him. His identity shall be struck from all records and histories. Memory will hide in the shadows, refusing to record the name of the owner to any who meet him...

This reminds me of that Jhereg in the Vlad Taltos books by Steven Z Brust who no one ever notices. He's not being stealthy, he's not invisible, he's just not that noticeable. He could be in the room with you, but he just doesn't have any presence. They even mentioned he had to join the Jheregs because back when he was with his old House, he would lead people into battle, but they would lose track of him, or forget he was there, and his forces would disintegrate.

Yeah, it's like that; though it's a magical amplification of that.

Somewhat similar effect to the Oblivion Item: the Gray Cowl.

Oblivion Wiki wrote:

...Whosoever wears it shall be lost in the shadows. His true nature shall be unknown to all who meet him. His identity shall be struck from all records and histories. Memory will hide in the shadows, refusing to record the name of the owner to any who meet him...

Yeah; that too.

Yeah but if say

You can't remember anything about him, to the extent that you can't remember that he just stabbed you (and thus have no reason to target him), you might be better off using invisiblity

He's so utterly innocuous you can't remember a thing about his face no matter how hard you try.

SNIP
How would you quantify that per 3.5 rules?

You're either modifying memories as suggested above, or simply stopping the formation of new ones, which is more likely.

I'd say, with detect thoughts at 2nd level and modify memory at 4th, then some sort of veil of forgetability comes in about 3rd. Should be on the Wiz/Sor and Assassin lists.

It is definitely a mind-affecting Enchantment (Charm), probably lasting for about 1 min./level. Will Save overcomes the spell, but on a sliding scale. Interacting directly with the target gives you bonuses to overcome the effect (+1 per round of interaction beyond the first), while simply walking by him on the street offers a severe penalty. Greater success on the DC offers more information.

Perhaps you could determine how many "facts" (race, height, gender, general appearance, facial details, dress, etc.) are masked, and then scale them in terms of difficulty and apply that to the Save DC scale. A better Will Save means anyone observing the target of the spell remembers more details. Failure means that you can't even really recall that someone walked up to you and asked for quick directions to the nearest tavern.

HTH,

Rez

EDIT - Just occurred to me to mention that in my version the "Target" of the spell is the person wishing to remain innocuous, rather than the person you are hoping doesn't remember you.

Also, a glamor might work, but then you are just having "general" features, but then you simply "look average". For someone to actually not remember what you looked like then you need an Enchantment.

/EDIT

Yeah; that too.

His face isn't hidden though; it's just amnesia inducing.

The Curse of the Grey Cowl is active regardless of whether you're wearing it or not, simply possessing it is enough to be effected.

The guy you meet wearing it has tried to announce himself to his wife, but she didn't (couldn't) hear his name or recognize him.

You meet him without the cowl on, and your character never recognizes him.

Of course, that curse is more pervasive, striking all references to the wearer from reality. Essentially he could stand right next to a portrait of himself and no one would notice the resemblance, even if they'd grown up with him.

It is definitely a mind-affecting Enchantment (Charm), probably lasting for about 1 min./level. Will Save overcomes the spell, but on a sliding scale. Interacting directly with the target gives you bonuses to overcome the effect (+1 per round of interaction beyond the first), while simply walking by him on the street offers a severe penalty. Greater success on the DC offers more information.

Perhaps you could determine how many "facts" (race, height, gender, general appearance, facial details, dress, etc.) are masked, and then scale them in terms of difficulty and apply that to the Save DC scale. A better Will Save means anyone observing the target of the spell remembers more details. Failure means that you can't even really recall that someone walked up to you and asked for quick directions to the nearest tavern.

This is an extremely minor quibble, but I would suggest using a different mechanic than the success of the saving throw. Say a successful save allows a Wisdom check or Spot check (Perception in PFRPG is even more appropriate), with a sliding scale of success. There simple isn't a precedent I know of for a sliding scale of success based on a saving throw. Requiring the observer to make two checks to learn something about the veiled subject makes the spell a little more powerful, yes, but if they fail the first roll, they get nothing; if they make it, they should at least get something with the subsequent skill or ability check.

Yeah, it's like that; though it's a magical amplification of that.

He's not invisible, you just don't. Remember. Anything. About. Him.

There was a second edition item that did this. A cloak of nondescription or somesuch. I'll hunt it down, but I want to say it was in the Thieves splatbook.

For 3.5 modify memory is the best thing to go with, imo. It does just what you want it to do, I'd just crank the DC up there, and have the guy wear some kind of cheap mask just to make sure...

It's got a _Ghost in the Shell: Stand Alone Complex_ Laughing Man vibe to it.

-Ben.

Edit: Realized I forgot to comment on the 3.5 mechanic.

I think I'll....
(spoilered for my pbp)