Doppelgänger

Description
Doppelgänger is a monster that emulates the appearance of anyone looking at them. That is to say that in a room full of twenty people, each person will see their own doppelganger, so Doppelgänger will have twenty-one different appearances, including their own, true appearance.

Doppelgänger's true appearance cannot in any way be recorded, as it is completely transparent when viewed through a mirror, meaning photography and film do not work. From Doppelgänger's descriptions of themself, they have nine multipurpose limbs and at least four eyes.

Due to the fact that Doppelgänger is only a certain actual size, they cannot effectively emulate very large or very small people. While Doppelgänger will still look exactly like these people when they look at them, there will be a large amount of area where the appearance and the physical existence do not match. For example, there may be areas on a very large doppelganger appearance that appear to be there, but swinging anything at that area will simply go right through the image. To a much smaller person, they may run into an invisible 'wall' when trying to go near the image of themself.

In the case of paradoxical emulation, Doppelgänger will not show any appearance whatsoever, and will instead remain completely transparent.

Using a powder or liquid to attempt to see Doppelgänger's true form would prove entirely fruitless, as they can choose to also emulate specific things for a limited period of time, such as liquid dumped on them, or the wall behind them.

Doppelgänger will be weakened more and more as more people look at them. Since each new person looking at them means they must generate a new appearance, and have that appearance match their own movements, even having five viewers can be quite tasking. Doppelgänger will avoid large social situations whenever possible.

Doppelgänger lives in several small caves they have dug around the Underground. They never stay in one cave for more than a month, and are constantly traveling around. They try to avoid people as much as possible in order to not have to deal with the uneasy and confused looks of others.

In terms of personality, the best way to describe Doppelgänger would be unpredictable. While often they avoid all social interaction, on occasion they have specifically sought it. When they seek social interaction, the intent can vary from pranking to torture to fulfilling sexual desires.

Trivia

 * Doppelgänger knows what the inside of a perfect sphere of mirrors with no interfering objects looks like.