Anytime anyone suggests anything is inherently evil - a form of music, a type of sport, a type of drink or anything else - what they are essentially saying is the devil created it. That's a lie.
- No thing can be good or evil - it can be put to good use or evil use, but to suggest that any thing itself bears an inherent mark of darkness is to entirely overstate the devil's power. It glorifies him in way that he certainly does not deserve.
- Secondly, even if some thing was evil, there is no power in the universe that can equal the power of God and there is nothing in this universe we are allowed to fear apart from God. In Isaiah 57:11 God lays this charge against his people: "Whom have you so dreaded and feared that you have not been true to me?" And, from a more famous passage, "...the one who is in you is greater than the one who is in the world" (1 John 4:4).
- The devil cannot create - he can only pervert God's creation. Even something like pornography is not a creation...its a perversion of God's awesome idea of real sex and love. Classic horror actually has a righteous use and is employed by the prophets at times but the sick vindictive splatter that's become popular is a perversion of our biology, our fears and a healthy reckoning of our mortality. None of these things are creations.

Halloween is actually a christian festival!
Our ignorance has led the contemporary church to oppose Halloween rather than use it - so we have 'light parties' and 'angel parties' instead as an alternative to what we see as celebrating darkness.
This wiki link will give you the full background but Halloween was originally instituted as a time to remembered the dead, the Saints who have gone before us and, especially, those who have been martyred. The use of skulls was adopted as a symbol to remind people of their mortality and that they will one day face God and judgement. Even the silly pumpkin lanterns have their origin in a silly folk story that warns against dealing with the devil.
So basically, all the religious fear and opposition to Halloween most of us have grown up with - it's a lot of rubbish.
Halloween - like Christmas and Easter - has been superimposed on top of dates that coincide with old pagan festivals, but they do not draw their traditions from those festivals. In fact the most evil thing about Halloween is the very thing it has in common with Christmas and Easter...the fact that it's been subverted to promoting consumerism. That was not the intention and actually flies against the very spirit Halloween is meant to stand for.
God himself makes these themes very clear in these passages from Isaiah: "I form the light and create darkness" - Isaiah 45:7
"I clothe the heavens with darkness" - Isaiah 50:3
And he alone claims to know the way to the gates of deepest darkness (Job 38:17).
Now, I've got my costume - how about yours?