Demonic Runes are an item dropped by monsters when a player has an elevated World Level.
Demonic runes must be sacrificed at a Sacrificial Pit to receive loot. This will open a demonic portal.
A demonic portal appears above the player's head rapidly raining down items. Demonic portals may "pause" if too many items are on the ground below them to allow players time to collect their items before they despawn.