I was surprised to see this thread. I am a catholic with a "Catholic Mezuzah".

I got a regular Mezuzah made of clear plastic and put in a scroll from Deuteronomy that has the prescribed texts. Then I wrapped a second scroll around that one, that contains the prologue from the holy gospel of St. John and other New Testament verses that witness to the Divinity of Christ.

I inserted both scrolls into the mezuzah and super glued a crucifix on the front.