SCP-303 acts to keep itself hidden and will resort to tactics such as using a fog/frost effect to ensure that no more than ten percent of its person will be seen at any given time. From what little description there is, SCP-303 is a sexless and emaciated humanoid with a head consisting of a large mouth. Its skin is described as reddish-brown and it is accompanied by heavy wheezing sounds. Its most unsettling quality is how it prompts a paralyzing bout of fear in any individual that observes it. Despite this, it is found that SCP-303 is allegedly not doing this on purpose and will not make contact with its observers.
SCP-303 also demonstrates teleportation and manifestation abilities in order to maintain its hidden status. However, it is shown that another observer will cause it to go into hiding.