After a somewhat different conquest and colonization of the Aztecs by the Spaniards (or any other European empire), which results in a much less severe decline, the population is gradually made to adopt Christianity, but the missionaries are unable to enforce correct interpretations of the dogma over a long period of time, and the colonial administration is busy with other problems and endeavors. It evolves into a very local flavor of Christianity, blended and overlapping with Aztec paganism in many ways.
The people worship "The God" and many Saints, but some of the small statues and idols commonly made of them look really weird, and there are many rituals and folk traditions no scholar of the bible could explain. On Christmas, the people celebrate, hang images of crosses all over their houses and in the streets. They make multiple man-shaped cakes from bread, honey and nuts, and at the end of the day cut them up and give pieces of this "body of Christ" to any guests or passersby.
Nobody is really sure what happens at Easter; the traditions seem to vary from village to village, although one common element is having people visit their friends and neighbors, dressed in animal skins, waving about crosses, and shouting "Merry Christmas!" as loudly as possible.
Parents often dress their children up in feathers and small makeshift uniforms before baptism - a questionable practice, but too harmless to be bothered with and if the priest makes a fuss they often perform a second, secret baptism themselves.
Like baptisms, burials are outwardly Christian, but still accompanied by many auxiliary rituals and superstitions. The dead are sometimes buried with a wooden cross in one hand and a shovel in the other one, presumably to dig themselves out on the hour of the Resurrection.
There are also whispers of darker traditions going on in isolated communities and remote settlements, where the colonial regime only occasionally comes to visit. Allegedly, when the crops failed, a child from the village was sacrificed to appease Saint Elijah; sometimes, it's an animal. And in the first days of December, they allegedly reenacted the betrayal of Christ by Judas and his subsequent crucifixion, with very real nails and crosses. According to some, these traditions continued underground as late as the 18th century, when they were finally driven out of existence or evolved into minor rituals simulated with objects rather then people.