I am a bit troubled by the idea that somehow October 31, Halloween, is a day that Satan claims. First, Satan has no claims. Second, every day offers the opportunity for evil. Third, ultimately even time itself belongs to God. Fourthly, I believe it is spiritually healthy for us to be reminded of monsters, demons, deranged people, and the dangers of this life. And last, It is good to celebrate life and community any time that we can.
Halloween, for me, is a time for facing our vulnerability to evil, but also remembering the All Saints Day which follows and reminds us our faith can and will sustain us no matter what comes our way. The saints overcame through faith and so can we.
God does not need defending. God is not offended by our imagination. Allowing the symbolism and activities of Halloween to be enjoyed does not help evil. Evil operates best when ignored or forgotten. Halloween is a good chance to give thought to evil and how God strengthens us to face it.