|• Acid breath|
• Breath attack
"Rust Dragons are known to hunt Gorgons, and live and feed in sulfur mines. With this appetite, Rust Dragons spew a concentrated acid as their primary attack. This acid is capable of eating through the strongest armor, lowering the defense of its target while inflicting further damage." AB manual
Acid breath special ability
Acid breath special ability may occur after a stack of Rust Dragons have attacked target creature stack and before the stack has a chance to retaliate. The breath reduces the target stack's defense by 3, and has 30 % chance to cause additional damage amount of 25 points per attacking unit.
Rust Dragons were added in Armageddon's Blade so there are no Rust Dragons or Sulfurous Lairs in Restoration of Erathia. They also prominently appear in the Rust Dragons scenario from the Dragon Slayer campaign in from Armageddon's Blade.
Tactics and info
Rust Dragons are true tanks; same defense as an Archangel and thrice the health, these dragons will endure much damage in early, mid-game and even some in late-game. In early game especially, it's pointless to fight them without Mighty Gorgons or powerful spells.
With a fixed damage of 50, same as an Angel or Archangel, and same attack stat as the latter, the Rust Dragons will usually deal less damage than expected. However, they are backed up by their toughness, speed and their very strategical ability, Acid breath, which reduces the target stack's defense for the rest of the battle, its effect being cumulative too. Keep in mind, they can also strike two troops, just like most dragons.
Efficiency and cost
For a significantly lower cost in gold than a Crystal Dragon's, the Rust Dragon's more "expensive" price to pay is the sulfur , especially for a Dungeon army. Unless having a large amount of special resources, if playing with a Dungeon army you might not want to recruit more than one for the tactical advantage. Otherwise, it's a good addition for its price, as any neutral dragon.
The strategy of a Rust Dragon is simple: block shooters, lower defense of enemy troops and soak retaliations. Aside from their powerful stats, they are vulnerable to spells, so beware of Implosion if you don't have more than 2 such dragons.
If the enemy army is more of a threat and these dragons' numbers are low, you shouldn't prioritize them too much. To fight them, it's needed to have high stats and many high level troops, so they can deal enough damage to kill them. As said before, spells such as Implosion are good.
Due to their raw strength, Rust Dragons don't get too much of a benefit from hero skills, aside from maybe Offense, since their damage is relatively low.
With their incredibly high speed, health, and attack damage, Rust Dragons are generally considered the third strongest creatures in the game, following only Azure Dragons and Crystal Dragons in raw stats.
Even though in the game files themselves the Rust Dragon and other neutral dragons are considered to be level 7, the official editor shows they are level 10 (8 for Faerie Dragon). This is either due to code limitations and impossibility of creating a unit with tier higher than 7, either because the developers didn't have time, motivation or reason to add a new creature level in the game code and invest time in that, just telling us they are level 10, respectively 8. As such, even now their levels are still being debated.