Just some ideas.
1. A little boy whose little boy fears (monsters hiding under the bed and in the closet, mistaking shadows of ordinary items to belong to other monsters, just the dark in general) are all justified. If an object or jumble of objects has a shadow that looks like a monster to him, said object turns into one. If he hears strange noises in the dark, whatever made them, again, turns into a monster, or at the very least someone out to get him. And if he ever has to sleep on a regular bed or near a closet, as soon as it goes dark, well, monsters. While the ones that are just a case of mistaken identity are just random monsters, the ones under his bed and in his closet are specific, recurring ones that would be labeled SCP-XXX-1 and 2. All of the monsters either revert to their real form or disappear altogether in light as bright or brighter than an ordinary nightlight.
2. A small clockwork machine (not related to the Broken God) with a human eye fastened in one spot. The machine has a series of knobs, levers, and other adjustable things, though only the Foundation has only found a use for a couple. When the eye sees an object it sort of "records" it, and after it sees it it can bring the object back to the present. Example: The eye-machine is placed in a room where a gun is fired so it can clearly see the gun and the bullet. The bullet has no obstacles in its path and just ends up in the other wall. Then the gun is removed and a person is placed in the bullet's path. A few knobs are turned and the bullet is brought back from the past on its same path, but this time because the man is in its path the man gets shot. And as a bonus or two, when a light is shone in the eye it dilates, and when it's set to bring back the very first thing it saw, all it shows is a mirror reflecting itself and an old, silent man who doesn't have either of his eyes.
3. An object shaped like a drop of rain that shifts the state of matter of the objects around it based on changes in temperature. If it gets hotter solids turn to liquids, liquids to gases, and gases to solids, while if it gets colder the reverse happens. The thing doesn't just heat or cool objects enough that they melt or freeze, though. The state of matter is the only thing that changes, and something that shifts because of it will have the same temperature it did before the change. It only shifts things within a certain area, whose size depends on the temperature change, to stop things like the whole room suddenly getting flooded or encased in solid air.
4. An object that takes up negative space. It appears to be perfectly black without any texture, but it's, well, not. It's less like looking at a picture of a black circle drawn on a piece of paper and more like looking at a circle shaped hole cut out of it. Or maybe it's something like an infection that affects things like objects and people and leaves nothing but the "holes".
Item #: SCP-XXX
Object Class: Euclid
Special Containment Procedures: All documented cases of SCP-XXX are to be hidden from public view by any means possible. Cases in urban areas are to have various public installments such as statues or fountains built over them if found in a public place. Any and all people aware of the case prior to concealment are to be detained while the SCP is being hidden and given class A amnesiacs before being released. Any private or abandoned residences where SCP-XXX is found are to be kept hidden by having the SCP itself be blocked off by high security doors, disguised to appear as regular wooden doors and opened by a discreet keypad placed in another area so as to appear like a regular thermostat. The buildings themselves are to be condemned. All residents of these buildings are to be evicted and given class A amnesiacs.
Areas far from civilization where cases of SCP-XXX are found are to be closed off. These areas are to be disguised as military encampments and research bases, and will be guarded by several Foundation personnel. The cases themselves are to be enclosed in tents to prevent them from being viewed by satellite or other long ranged viewing equipment.
In the case that an object affected by SCP-XXX is well-known among the people nearby, the Foundation is to prepare several falsified records describing the objects destruction and reasons for it. People affected by SCP-XXX will be investigated in order to determine their identity prior to their condition, with records describing the individual in questions death to be made upon that discovery.
The installments, buildings, and camps are to be visited and checked upon on a monthly basis by Foundation personnel. No other personnel are needed other than the aforementioned guards stationed at the camps. See Adendum XXX-B. All documented cases are to be monitored at all times by Foundation personnel. Researchers are to be stationed at each camp for examination. Public installments used to conceal cases of SCP-XXX are to be updated and have security cameras installed within to monitor the cases, with researchers stationed within the area to monitor the feed. Buildings in which cases are hidden are to have researchers living within to monitor the cases in person.
Description: SCP-XXX is a condition in which an object or person appears to be replaced by an entirely black, textureless silhouette frozen in time. This is not the case, however, as the black figures supposedly left behind are anomalous in nature. Objects affected by SCP-XXX don't have an actual texture because they aren't made up of matter, and are instead the complete absence of it. They only appear to be black because light simply disappears within them, similar to the effect of a black hole, as do most objects dropped within. People have been able to insert parts of themselves within and take them back out without any ill effect, but as their doesn't seem to be a clear "ground" within and many of the cases of SCP-XXX are too small for most people to fit into, no explorations "inside" have been made. Foundation researchers have described it as being "less like looking at a picture of a circle drawn on paper and more like looking at a circle shaped hole cut out of it".
As of yet there is no way to determine when and where cases of SCP-XXX will appear. The Foundation has stationed several Agents in each major city in order to react quickly to any possible sightings.
As the Foundation has only been able to act after sightings of SCP-XXX, the details surrounding their forming are for the most part a mystery. The only clue is that the few witnesses able to observe a transformation describe it as being instantaneous, with the objects in question being "perfectly normal one minute, and then, in less than a second, pitch black and frozen in place".
Because at this time there seem to be no ill effects of exposure to objects affected by SCP-XXX, many of them will be left unattended with only monthly check-ups to make sure the areas are secure. See Addendum XXX-B
Addendum XXX-B: On -random date-, at the site of SCP-XXX-4, one of the guards stationed at the site reported hearing unusual things. Another guard was sent to SCP-XXX-4 to check for signs of intruders. Guard did not see anything out of the ordinary outside the tent, but upon entering he reported seeing [DATA EXPUNGED]. Researchers are to be sent to all other sites in order to observe the other cases full time.