It obviously comes in peace.
Shadow Creatures are demonic spirits that crossed over to the realm of the living when Robert opened a portal to the spirit realm. They can only be seen and combated using Robert's Smartphone. Like the Black Widow, the Shadow Creatures are weak to light and can be defeated by shining the Flashlight on them until they disappear.
Some Shadow Creatures possess items and the only way to get those items is to defeat the monsters.