There is absolutely no part of him that is stupid enough to not recognize 'attack me' as a set up of some stripe. Especially not from an asshole with a holy avenger and a griffon.

Who is a healer, who wants to be in Gotham for Reasons and Bruce intends to let be in Gotham -also for reasons.

He's still going to do it.

He has a serious problem with curiosity.

So he draws back, those shadows solidify even more around him and then lash out, hard and fast at Zerxus with, for all intents and purposes as though they have taken physical, cutting, form.

Fire? Nah. He's much more into the dark. ...and just a touch safer.