Prayer in Fight

In order to use something like Hindrance in a fight, does the priest need to be engaged with the target/targets? Or can he stand at the edge of battle and pray to hinder his foes and help his allies?

Yes, if you’re affecting an enemy in a combat situation, you must engage.

Thank you!

Will no one rid me of this turbulent priest?

It depends. How much are you willing to pay, Your Majesty?