If you're not going to draw upon enhanced durability when you're batted around and set on fire, what are you holding it for?
Agreed. It isn't like Christos hasn't had opportunity. And surely other wizards would recognise signs of demonic influence. The brimstone smell alone...let alone subtler things.
I just can't see it being any of the Senior Council to be honest. I did hypothesise based on the OP question though. Maybe Ancient Mai just for the reveal factor...but why would she bother? Also it wouldn't add up with any of them having a Coin considering earlier things in the series. The Gatekeeper seems to trust them all and points out that while the Council is harsh it can be necessary at times.
