The ancient Druids of Ireland, who were the pagan priests of the age, celebrated Samhain, which was a time when the dead, demon and evil spirits alike were believed to be able to have a greater influence upon the world of the living. As such it was a time of fear and the people were encouraged to disguise themselves as monsters and evil spirits so that the real demons would pass them by, thinking they were fellow denizens of darkness.
1 Thessalonians 5:22: "From all appearance of evil refrain yourselves."
Don't encourage trick or treaters either. Turn the lights off, or if you have the guts, admonish or rebuke each and every one that comes to your door.
As a side note: This principle of avoidance obviously applies equally to anything that proposes itself as a form of entertainment (which is what Halloween does) and which also promotes, encourages or makes light or fun of condemned elements such as sorcery, magic, wizardry, witchcraft, etc.
So most anime is off limits to Catholics, as is Harry Potter, Star Wars and the like. Do you think that continually exposing yourself or your children to things God has marked as abominable is good entertainment? Do you think you will be able to persevere in virtue and justice if you seek enjoyment in such things? If so... do you really want to make me weep?
Note: I probably won't actually weep, but rather mournfully lament the loss of your soul, and think you are pretty foolish to lose it for something so stupid.