Hints:
1. Send down a thief (do you have Imoen?) who has good backstabbing damage (esp. Sword of Backstabbing,) and do damage on the main priest. then send down your other guys.
2. I would resurrect the dead guys at the nearest temple, they willl help.
3. Give one character really good armor, rings, allthat, then cover him/her in protective spells. Have themm attack demon and draw him off, while the other guys kill the preists.
Good Luck!
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Official teaser and ranger of the HADB Clan
"Evil round every corner...careful not to step in any."-Minsc
"Gimme a sword, I'll win this war for you!"-Mad Martigan