(at around 43 mins) When Billy the Kid bites the girl laying on his lap, the bite marks and blood (when viewed from girl's right profile) are located in the center of the throat. A few seconds later, when viewed from above, the bite marks and blood have moved 2 or 3 inches to the left.
(at around 4 mins) Newton is said to have come from Chicago to Montana to get a news story on "the Wild West." The Wild West being an immensely romanticized myth notwithstanding, during that time, it was not referred to as "the Wild West."
(at around 19 mins) When Rayne finds Bernadette and Vince lying dead in the snow they are completely clean, even though it is snowing and they were killed the previous night (or perhaps longer.)
(at around 1h 30 mins) Early in the movie, it is explicitly stated that bullets have no effect on Billy the Kid; however, in the final gunfight, he is shot by a chain gun and is severely injured by it.
Billy the Kid's ultimate plan makes no sense, and in fact, is ultra-self-destructive. He plans to use the ever-expanding railroad system to spread his vampire "children" all over the country until all the humans are killed or transformed. If he accomplished this, he and all of his brethren would die of starvation because they would no longer have humans to feed upon.