Knowing: opt-in, baby! A quick list of details that would be fun to Know: completely horrible & verbally abusive dad, hugely influential magician who's worked with the upper levels of government, served in the Napoleonic wars, has an on again/off again friendship/partnership/hatemance with his former tutor Gilbert Norrell, super happily married, probably will never see his wife again, cursed as hell, likes cats, loathes pineapple. Notably, Strange is Dark coded (said curse is him trapped in a pillar of eternal darkness, centered on him) and Spiral coded (he intentionally made himself mad in order to do a neat piece of magic) as FUCK.
Compelling: absolutely! man's got zero mental defenses.
Beholding: also yes! Strange is the sort of guy to accidentally stumble into things without realizing the consequences, so I could definitely see him giving John a statement should their CR swing that way.
no subject