First idea: Stairway to Heaven (working title) - A Great Depression era farmer and his occult friend attempt to contact a deity to end their starvation. They eventually do, but need to be a certain altitude to actually speak with it, so they build an anomalous staircase in the middle of a field and punch through to the creature's dimension.
The SCP itself is the stairway, which causes auditory and visual hallucinations as you climb it. I'm not quite sure what should happen when you get to the top, but it should evoke a fear of heights, since that's what I'm going for. Additionally I want to imply that whatever the two men contacted is not the Abrahamic god, but a malevolent entity that is purposely flooding the minds of the people on the stairway with angelic (but terrifying) imagery in order to make it look harmless.
Second idea: The Mirror. The Foundation find a technologically advanced artifact resembling an Ubaid-period Sumerian copper mirror, which is constantly sending and receiving messages from an unknown location on Earth, and constantly sending and receiving signals to a location somewhere in the Kuiper belt. A clay tablet recovered from the same place as the mirror that states a message in both Sumerian and an unknown alien language acts as a "rosetta stone" that allows the Foundation to partially translate the fragmented transmissions going to and from the mirror.
The transmissions would talk about an unknown alien group quarantining humanity due to their anomalous ability to create anomalous objects - In short, an alien rough counterpart of the Foundation has designated humanity their version of an SCP, and the Kuiper belt object is their method of containing us. The translation would end with a transmission from somewhere on Earth to the mirror about how humanity has the ability to create, attract or otherwise gain access to potentially reality-destroying artifacts, and a request to destroy humanity to prevent them from generating more. To create ambiguity, there wouldn't be a response to the request.
Third and final idea: The Great Bull. Gugalanna is a Sumerian winged bull-deity that plays a part in the Epic of Gilgamesh and Inanna's Descent into the Underworld. In the original myths, the timeline is something like this:
-Gilgamesh rejects Inanna
-Inanna goes to the other gods to request Gugalanna attack Gilgamesh's city in revenge, threatening to raise the dead to "eat the living" if she doesn't have her way.
-Gugalanna is sent to Gilgamesh's city to kill him
-Gugalanna is killed by Gilgamesh
-Later, Inanna descends into Irkalla (the underworld) to apologize to Ereshkigal (her sister, Gugalanna's wife and queen of Irkalla) for causing Gugalanna's death.
However, the idea behind this SCP is that the Sumerians got the myth wrong, and what actually happened was:
-Gilgamesh rejects Inanna
-Inanna successfully raises the dead (including Gugalanna, who was "dead" by virtue of residing in Irkalla with Ereshkigal) to attack Gilgamesh
-Inanna makes Gugalanna incapable of dying to make him a better weapon
-Gilgamesh severely wounds Gugalanna, causing him to escape.
-Later, Inanna descends into Irkalla to apologize to Ereshkigal for reviving Gugalanna and separating them.
So the skip would be Gugalanna, of course, still alive after a few thousand years. He can recover from any injury thanks to the way Inanna revived him, but his body is a rotting corpse and for whatever reason his healing abilities only slow down his decay, not stopping or undoing it. So Gugalanna decides that since in a few hundred years he will be completely immobilized from decay and he still won't be able to die and see Ereshkigal again, he needs to find somebody to kill him quickly. He attacks a large population center to provoke somebody into killing him, and the Foundation captures him. (By the way, non of this stuff about his origins or his motivations would be explicitly stated in the skip. It would only be implied by the fact that he's a Sumerian speaking winged bull with obvious signs of reanimation, who continually demands that "you will take me to her.")
Every time the Foundation seems to lose interest in him, he tries to break out again to make him seem like a threat and get them to kill him. Eventually he specifically targets the doctor in charge of researching him, breaking out and ignoring several large cities full of people to kill just so he can get to the city where the doctor lives. He kills the doctor's family to provoke him, but at the same time the doctor figures out what the bull's motivation is, and out of spite requests that any attempts to permanently terminate the bull be ceased immediately. (Again, the attack on the doctor's family would only be implied, by stating that "notably, it ignored several large population centers, including blackbox, blackbox and blackbox on its way to the city of blackbox", having the doctor's tone change from detached and clinical to barely-concealed-rage and repeatedly messing up translation due to distraction, and the bull ending the last interview with "how many people would you kill to be with them?")