Since the History Contest is over, I suppose this can be unveiled for all.
1. Whatever anomaly you are using should be something that can feasibly exist in the 19th century. If you are using an SCP whose article explicitly states that it exists OR becomes anomalous only during the 20th century onwards, no go. If the era of creation is not explicitly stated, go for it.
2. Since the Foundation was not a thing during Occult War i, do give any SCPs you're using another name when referring to them in Phenomenon and/or Description.
3. You are free to use anomalies outside of SCPs. You can totally reference anomalies solely mentioned in Tales or GoI articles, so long they satisfy Rule 1.
4. History repeats itself. Try to write such that things are more or less similar (to a very uncanny level) in the previous and current realities.
5. Group the phenomena according to region.
6. The context here is ultimately a war, so let that be a framing device for how you can write your entries.
7. Note that the in-universe writers of these entries are the original O5 Council in Wrong Proposal. The writing is ultimately from their POV. Also, at the time of Occult War i, they were still in their original organisations.
As with every collab page, this is subject to pruning every now and then.
This is my first collaboration page, so let us collaborate.