cleric vs artificer

[limejuicepowder]

A major battle is about to start in the campaign I'm running. The PC's are leading the defense of an entire city - the BBEG, an artificer, just showed up at the end of the last session.

Riding a flying carpet, he cast a spell from a book made all of the defenders at the gate throw up a demonic egg that hatched in to a (modified) dretch - if they were lucky. Failed save means the dretch comes exploding out of the poor soldier's chest, a la alien. 6 hill giants then assaulted the main gate.

Anyways, the players have their hands full. The BBEG is attacking the city in order to recover some runestones the PC's took from him in a previous encounter. The stones are being held in the church of odin, guarded by one of the PCs and the archbishop, a 10th level cleric.

How should I have the cleric fight? I'm using the NPC cleric stats from the DMG for him, though I'm willing to change his spells around if the situation calls for it. I'm just a bit lost on how the cleric will do anything, since the artificer could kill him in a single magic-missle filled round. There's a possibility one of the PC's will be there for the fight, a 6th level crusader.

The BBEG is level 7, though he has items that are somewhat above WBL.

TL;DR: what tactics should a lvl 10 cleric use to not get wasted by an artificer's blasting in 1 round?

[Spacewolf]

Well if the ground is hallowed that gives a +2 bonus to delfection and saves and allows no summoning plus you can add certain spells to it link (http://www.d20srd.org/srd/spells/hallow.htm), spell immunity against magic missle and one other spell of your choice, that should give the cleric at least a good chance i would say

edit although im not sure if spell immunity would work so maybe add on entropic sheild (not sure if that would work either but i think it should as magic missle is a ranged attack), Divine power for some extra HP plus strength, hold person if the cleric gets init would stop the BBEG in his tracks, glyph of pain and slumber could also be preperpared in the church which could cause some problems for the villain as well.

Theres some quick ideas that may work

[Elric VIII]

Nightshield from SpC gives immunity to Magic Missile.

[Snowbluff]

What happens to an Artificer if you disjunction him?

AMF would give the Cleric an edge over the artificer. Clerics have better BaB, Health, and actually wear armor.