[Suzerain of Sheol]

Sorry if there was any confusion, Arcane Knowledge is knowing things like "small arms fire is useless against Dybbuk" on through "A Cherub's most potent offense is its ability to fire thousands of lightning bolts from the eyes on its wings" all the way up to "Spiritual attacks are ineffective against Rephaim as they're composed of multiple redundant souls". It's working knowledge of how to survive all these supernatural horrors, not really similar to Knowledge (Arcana) from D&D or anything similar that focuses purely on the workings of magic.