I'm considering nicking the rules for Divine Combat from the version of this in another forum.
It's basically rolling a 1d10, adding modifiers for various artifacts and such*, then seeing who got the higher number.
*Such as divine weapons, being in a place strong for your domain, expending motes, and the rank you have.
“She'd become a governess. It was one of the few jobs a known lady could do. And she'd taken to it well. She'd sworn that if she did indeed ever find herself dancing on rooftops with chimney sweeps she'd beat herself to death with her own umbrella.”
― Hogfather