The boss fight inside the church is one of the most devious in Dark Souls. While there is a respawning painting assassin NPC during the fight, the main boss is... another player. Yes. I hope you've been practicing your PvP skills because one of the many crazies who enjoy ruining the day for others will be summoned as "your boss fight", and given the people who sign up for this covenant would be the ones who PvP at every opportunity - lets just say are not novices.
Said opponent cannot use Estus heals which is great, but everything else in their arsenal seems to be ok. They also get an AoE spear summon and an automated magic spear spell hovering above them (at least I think its automated). The "Spears of the Church" Faltran and Bloodfire did their duty of blocking my progress. Rather than hoping one will just throw the fight (which probably isn't going to happen, given the game) I decided to tilt the battle to my favor as much as possible, summoning sunbro Andraste to assist and coating my axe with the bleed buff.
Pre-combat shot. The fighting is too intense later to take screenies.
Spear of the Church Anayaki still put up a good fight, but with my tricks and a late "suddenly switch opponent" tactic by Andraste and me, Anayaki was caught unprepared for an axe to the back. Being unsure of who to block against next ensured both of us hit which ended the boss fight in our victory. Thank you Andraste! Funny that someone named after a goddess/saint helped me get through this section! ;)