The black dragon is a fourth-level creature from the Asylum town in Heroes of Might and Magic IV. Black Dragons are the mightiest and most expensive creatures available for the Chaos/Asylum Faction. Their biggest advantage is also their greatest weakness: It's totally Immune to Magic, even your own magic. So casting Bless/Haste or other beneficial spells on them doesn't work. This also means you can pound the area with Armageddon spells without any risk of hurting them.