The Soul Vial is an item added by the Ender IO mod. Right-clicking a mob will put the mob in the item, and right-clicking it again will release the mob from the Soul Vial. This does not consume the Soul Vial. Combining a Soul Vial that has a mob in it with a Broken Spawner in a Soul Binder with 15 levels will change the mob type of the spawner. A Soul Vial with an Enderman inside it is required to make an Ender Crystal in the Soul Binder.