A few armies, notably the Vampire Counts, have a few Ethereal units.
Normally, swinging a sword will just pass straight through them.
However, Magically enhanced weapons, such as the Chaos Knights 'Ensorcelled Weapons' are able to wound such creatures.
More often than not, there is a special effect to go with the Magic Weapon, but this is not always the case, and can just be an "Ordinary Magic Weapon". Using Chaos Knights as an example, they gain +1 Strength, and are capable of wounding the Ethereal Creatures. However, a unit of High Elves, joined by a Character carrying the 'Amulet of Light' recieve the benefits as normal from their halberds, but are also capable of making Magical attacks, but they do not have any additional benefit.
Needless to say, any Magic Weapons that a Character is carrying (either one that is a bought from the Race Specific Magic Items list, the Common Magic Items List, or any that Special Characters carry) count as Magic Weapons in all regards - although they usually have funky special rules to go with them; Sunfang, Ghal Maraz, and Slayer of Kings most notably.
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