There isn't as much imagery lifted directly from slasher movies. It's quite PG. But there are generic devils and witches, etc, and plenty of scarier characters from movies (Joker, Chucky) as well as creepy clowns, killer clowns, zombies, grim reapers, plague doctors, corpse brides, creepy dolls, red eyed ghouls, angler fish, werewolves... One Hallowe'en I gave out candy to a lad dressed as a pimp who was accompanied by several 'ho's'. To balance that out, there were dozens of kids in home made costumes. The best was imo a mime.
"Christians" is an umbrella term.
Fundamentalists tend to shun Hallowe'en. English Christian fundamentalists a few centuries ago also banned the celebration of Christmas. Baptists that I know have all sorts of strange certainties about it (e.g. "it's the devil's birthday").
This may be impressionistic, but Catholics tend to accept it with gusto. Mexican Catholics in particular have their own Dia de Los Muertos celebrations that are very explicit in their focus on death and spirits and the liminal element of the feast. The skull is a very prominent motif of Dia de Los Muertos.
This is grist to the mill of some fundamentalists, who think Catholics are Satanists and doomed to hell. The more militant among them refer to Mary as the whore of Babylon, and the pope as the anti Christ. They also hate Jews, Muslims, and actually anyone who isn't one of them. Everyone else is a tool of the devil.
When my DCs were in elementary school (RC parochial school) they were allowed to wear their costumes to school, minus masks and with no weapons, heavy accessories, or 'excessive' gore permitted. There was always a school Mass the next day (All Saints Day).