Dungeon. The key word is "shadow," and a shadow is impossible without light! The Fury is the best unit in the Dungeon... Reimagined harpies...
Shadow exists even where there is no light; it's just usually called darkness. But the developers decided that "League of Shadows" sounds better than "League of Darkness," and besides, what light is there in a dungeon? Dark elves, as is well known, have eyes that see in the infrared spectrum, so they don't need light.
Furies are good if they aren't attacked by archers before they can attack someone, otherwise, you end up with a bunch of Furies lost without any benefit.