ToME WikiOrvin: How about a disguise skill or ability that causes monsters to believe you are of their same faction? Maybe, restrict the use of disguise to humanoids trying to appear as other humanoids? This could also be used on shopkeepers to get better prices.
RavenRed: There is, as well, Tolkienian precedent, with Sam and Frodo getting into Mordor through disguising themselves as orcs.
In terms of Game Mechanics, I'd have "Disguise" as a new ability (free to Rogues), goverened by the player's Sneakiness skill.
You select a monster (limited to those with Humanoid body type) and you can try to "clone" their faction. This could then be checked against all the similar factioned monsters in the vicinity. It should be more or less timer based, as inconsistencies would begin to show up after time. After that, your faction would return to normal, with possibly an aggravate thrown in as your subterfuge is detected. This isn't a long-term deception, but a tool for sneaking past/up to hostile monsters.
- % Chance of Detection = ((Sneakiness skill x 2) +10 - (Monster Level (-10 if SMART, +10 if stupid or weird mind, +20 if empty-mimd)) - (Turns since Disguise adopted / 10))
NeilStevens: If we want this I'd rather make it a feature of mimicry.
RavenRed: Now THAT is an excellent idea. You could also perhaps extend the ability to non-humanoid forms at L40 or so...
KhymChanur: Maybe I'm just thinking about this too hard, but if monsters can tell that you're not "one of them" when possessing one of their corpses, then how are you supposed to fool them by mere mimicry? Maybe it can be some sort of mental ability, were the right frame of mind, or projecting the right attitude, or something similar, would fool them.
NeilStevens: Mimicry IS in large part the art of deception. Mimicry played a large role in Tolkien's works in that manner, for example when Beren and Luthien went to Angband, in the quest for the Iron Crown that inspired ToME's own ancestor.