It most certainly is. Anything that celebrates darkness is of Satan, but Halloween is especially evil because it is the "holiest" day for the false religions of Wicca and Satanism. I used to think Halloween was just fun and games and dressing up to be spooky nowadays and it was only bad in the past, but then I learned that on Halloween, dark witches cast spells to conjure demons and most often succeed. There is more info here.