The Mist

Dark Misty Capital. Jack, a problem, filled up with too many abilities. One of them is this Boundary Field Noble Phantasm. A sort of phenomenon turned into a Noble Phantasm. It scatters a mist of sulfuric acid over a radius of dozens of meters. It deals damage over time to ordinary people, and it also makes it difficult for magi to use magecraft if they don't take countermeasures. Servants only drop a rank in agility, but it is extremely difficult for them to see and track Jack within the mist.
It originally stems from the smog problem that used to occur in London. The soot and smoke that increased rapidly due to the Industrial Revolution mixed in with London's cold fog, giving it acidic qualities that caused an enormous outbreak of victims.
Even in 19th Century London, the problem was already becoming quite serious, and the serial killer Jack took advantage of the fog to attack prostitutes.
Thanks to this Noble Phantasm, Jack can almost unconditionally fulfill one of the three criteria of her other Noble Phantasm—that it must be deployed in a “place enshrouded by fog.”

Fate/Apocrypha material: Fate/Apocrypha Encylopedia