So, anyway, here are my ideas.
1. Potential Title: "A Scary Clown What Teleports Behind You"
So there's this humanoid being that has various anomalous traits that make it resemble a clown. (e.g. the ability to alter its skin colour to resemble makeup, the ability to summon clown-related paraphernalia, etc.) as well as the ability to teleport certain distances. (I'm going to keep that distance relatively small, so that the Foundation can contain it with sufficiently thick walls.)
The twist on the standard "Monster Clown" gimmick is that it is completely innocent. It genuinely wants to cheer people up, and it genuinely believes that having a clown come out of nowhere is a good way to do that. One day, there's an incident where it gets out, and sneaks up on a low-level researcher or agent. They're scared, the SCP is confused, and the agent/researcher, not knowing any better, explains to the SCP that clowns are generally seen as scary, not happy. The SCP has an existential crisis, becomes extremely depressed and starts mumbling about "just wanting to make people happy." Its despair and confusion about not knowing how to actually make people happy could be conveyed in an interview with a Foundation psychologist.
2. Potential Titles: "Wendy the Wondertrain" or "Wondertainment Prototypes"
As implied, the SCP is about Wondertainment building and producing sentient trains. (Originally I was going to go with Thomas the Tank Engine, but I scrapped that.) Only the Foundation doesn't have the finished product, they have the early prototypes and tests Wondertainment did. Everything from the first, initial attempts to graft human flesh onto a steam engine and make it live to a non-sapient but alive pseudo-"Wendy".
3. Potential Title: N/A
This is a very early idea. In fact, I don't even have the SCP itself planned, just the story that goes around it. The SCP would be a late Prometheus Labs project, started only about a year before its destruction. The story of its construction would be told through the journal of the P Labs scientist that heads the project. It would detail his/her initial excitement, gradually turning into despair and worry as news of other P Labs skips failing reaches him/her. Eventually the scientist decides to abandon the project and quit their job, assuming that it will go horribly wrong like everything else P Labs built, and before another person can be assigned to continue the project, Prometheus Labs is destroyed and its resources taken by the Foundation.
Only, it turns out that the abandoned skip the scientist was working on actually works perfectly, without any obvious flaws.
4. Potential Title: N/A
Two biological entities roughly the size of asteroids are in an orbit around the Sun that will cause them to collide with earth. Eventually the Foundation commandeers some resources from space agencies and throws a nuke at one to stop it from hitting Earth. It is destroyed and pushed off course, but it repairs itself and uses gas jets to alter its orbit and point itself at Earth again. Sensory organs capable of picking up radio waves emerge from its surface. After a few months, it then alters its orbit to point away from Earth and instead into the Sun. It then begins emitting light, presumably to communicate with the second entity. The second entity communicates back. The first entity rapidly increases the frequency of its messages, and eventually begins just repeating the same patterns over and over again. The second entity is still on an orbit that will lead to an encounter with Earth. Then, the first entity alters its orbit so that it will impact the second entity before it impacts Earth. The second entity tries to alter its orbit so that it will strike Earth and avoid the first entity, but it doesn't work, and the first entity slams itself into the second entity. Large tentacles emerge from the first entity and wrap around the second entity, and the first entity pulls it away from Earth. The entities are currently slowly falling towards the Sun, and have been declared either neutralized or safe.
5. Potential Title: "Stairway To Heaven"
An outdoor spiral staircase (I already have an image planned) that appears within a certain geographical area at random, and uses something (haven't decided yet, possibly visions of loved ones or lost children, but that's a little cliché) to lure people onto it. Once people are on the staircase, they vanish and appear on a stairway that's several times higher. (Like, above the clouds) People on the stairway show an extreme aversion to descending down to the ground below, (they usually cite that they'll fall) and a slight reluctance to going further up. If they reach the top, they vanish. The Foundation doesn't know what happens to them, but I'm planning on heavily implying that they encounter whatever extradimensional being created the stairway. This one is a little weak story-wise, but I'm hoping it can be held by interviews with D-Class put onto the stairway, and the acrophobia they experience, entirely based on my personal fear of heights.
6. Potential Titles: "Alien Abduction", "Unidentified Flying Owls", "Alien Parliament" or something much better than those three which I haven't thought of yet.
Two cultural memes have anomalous properties: The concept of "alien abductions" and the concept of owls as "death omens". People who genuinely believe that either aliens abduct people or that the presence of an owl is bad luck in some way have a small chance to cause an anomalous event while they are asleep. During the event, several large owls (or owl-like creatures) will emerge from unobserved locations and converge on the sleeping person. The owls will grab the person in their talons, carry them to an unobserved location and vanish. Some time before sunrise, the person will reappear, unable to remember what happened when the owls took them away.
The truth is, these owls aren't created by the beliefs of the person, they're sent to the person who believes in alien abductions or owl omens by extraterrestrial and/or extradimensional beings, who want to keep their existence a secret. These other beings are running their equivalent of a keyword search through the minds of every human being on the planet, and when stuff like "abducted by creatures" or "owl are evil" comes up, they send their scouts, disguised as owls, to take a more detailed look at their target's brain. When it turns out the person is just a conspiracy theorist or believes in omens, and is nowhere near the truth of the matter, they let them go. However if, for example, the Foundation convinced a D-Class that these beings exist, the owls would take the D-Class and not bring him/her back, or bring back the remains.
Collapsed that for you. —Drewbear