The document starts warning you that the files are Level 4 classified. A memetic kill agent appears, you get a basic description like any other article, and you find an addendum titled "Recovered Chaos Insurgency Files"
These files describe the discovery of the substance by the Chaos Insurgency in the ███████ Caves in Thailand. It turns out reptile skeletons are producing it, and are causing various bats in the cave to mutate into mindless, gargantuan reptilian-humanoid beasts. The Insurgency take the beasts down and recover 50 liters of the substance.
As the Insurgency is basically a Foundation without rules, testing immediately begins on the substance. First they start using small animals like rats, mice, bugs, but then they approve human testing.
Drinking it yields identical results to the small animal tests, yet injection starts to cause random effects in subjects. They try injection of the substance into infants all the way to seniors, all of which gain different mutations, some of which collapsed into puddles of the substance hours after creation. Testing continues, this time with small doses. These cause mental instability in subjects and later converts them into reptilian humanoids just as with a regular dose.
Testing continues despite objections from staff who are constantly terminated by a researcher's armed guards. This continues until the Foundation discovers the facility and raids it with an MTF squadron. After several members of the squad get mutated, the Foundation terminates the researcher and his guards, and takes the substance into their own hands.
Later, they decide to put it in SCP-914, on 1:1. All that comes out is a note with an illegible signature.
"They will return, the cold blooded friends of us. They will."