Red Dragon and Black Dragon
• Breath attack
• Immune to spells level 1–3
• Breath attack
• Immune to all spells
• Hates Titans
"Red and black dragons with their great mobility, flying ability, and powerful breath weapons are among the most effective units in the game. Red dragons are immune to spells below level four. Black dragons are twice as durable, do 150% damage to... titans, and are immune to all spells." RoE manual
Tactics and info
With the health value of 300, Black Dragon is one of the toughest creatures in the game. In the original Restoration of Erathia, it was toughest of the dragons and its health was only matched by Titans' and Ancient Behemoths' (and by Haspid's in Horn of the Abyss). It also has more Defense than either of those creatures. Armageddon's Blade expansion introduced four new dragons, Faerie Dragon, Rust Dragons, Crystal Dragons and Azure Dragons, which all are neutral creatures and have more health than Black Dragons.
Because of the Black Dragons' spell immunity, they are suitable to be used in tactics often called dragogeddon. In dragogeddon, a hero with preferably high power skill and Armageddon spell attacks with an army only consisting of creatures immune or very resilient to the Armageddon spell. The tactics may be used in "hit-and-run" tactic, to advance through wandering creatures or even to slay enemy heroes. In Restoration of Erathia series, Black Dragons were the best creature to use in dragogeddon.
The benefit of using Black Dragons in this tactics is their high initiative, in other words, their speed. Only Phoenixes and Gold Dragons are faster creatures that are immune to Armageddon. High initative enables hero to act first in the combat, and this way possibly win the battle before enemy gets a chance to flee, surrender or otherwise cause resistance.
Together with the Titan, the Black Dragon has become a symbol of the Heroes series since it first appeared in Heroes of Might and Magic II: The Succession Wars.
This spell immunity is a double-edged sword, though, as it makes both Red and Black dragons immune to most beneficial spells, including Resurrection. Placing Red or Black Dragons (as well as any living Dragons) in the Skeleton Transformer will give you Bone Dragons instead of regular Skeletons.
Both dragons are affected by Dispel.
Though it is stated in the manual, Black Dragons do not hate Giants.