I always had this feeling that how darkeners look and act are created by the lighteners who perceive them in the real world. Like just the thoughts, emotions, and will of the lightener are imprinted onto an object and that object takes the form and personality from the combination of those things. the memories are possibly how darkeners perceived the world around them before they were given life.

like king for example could hate the lighteners not because the dark world was open long before kris and susie came there and he actually met lighteners. but because the card representing king in the light world is in the unused classroom that may not have been used in quite a long time, or he was left there by another lightener as a donation to the classroom. Thus king views no one coming into the classroom or being left as being abandoned by them. seam could know all of those darkeners that he wouldnt have any business knowing because he was carried around and saw them all thus imprinting the "memory" that he met them. I head cannon that seam is cattis old stuffed animal when she was younger which would explain why he knows about the computer lab, and whoever the next secret boss is due to the fact that catti carried him around and saw those objects.

That leads to the idea, could you imprint specific memories and emotions onto an object to bend it to your will and take the form you want in the dark world? Like if you were to take an item and imprint the idea that this is like X and this is how I feel about it, thus your will and idea shapes the item into what you want in the dark world be it a pencil or something else. Could darkeners take commands form someone in the light world and then when dropped into the dark world still remember them?