Film sound familiar?

[robinbloke]

I'm trying to remember the name of a film that was on Sci Fi a while ago; it involved two guys vaguely fighting the forces of darkness after having to repet their sins in a church (scaring the hell out of a priest) there was a big ritual type thing near the end and the bad guy turns into a monster... it was all fairly tongue in cheek.
Vague, but then my memory isn't good.