Swamp Dragon/1.03.25

Swamp Dragons are elite fliers.

The Swamp Dragon is arguably the most feared Dragon in the eyes of Heroes, as the Swamp Dragon's ability to erode and lower armor cannot be undone! Even Dragonslayer class Heroes have to think carefully before fighting one, for even victory will have its cost. The standard Dragon was always a decent unit and the Swamp Dragon builds on from that. As you expect, it's just as useful as the Fire Dragon for its role, but with the addition of permanently weakening enemy infantry foolish enough to challenging it. Its breath attack can occasionally cause burning, too! In WBC3, the armor system was completely changed which, not only split armor into 2 categories, but made armor in general less effective than it once were. There's no doubt that the Swamp Dragon would have been considered broken if it existed in the past games. The only case when a Fire Dragon would be preferred is when crystal is scarce (Fire Dragon needs metal instead). In v1.03.25, Dragons get resistant to their breath attack's damage type. Both Fire and Swamp Dragons may thus divert and survive a few attacks from fire-using Titans: Iriki, Lord Bane, The Lion Throne, and Sirian.

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Barbarians
The Swamp Dragon's fire attack naturally lends it building razing capabilities, filling in the Barbarians' missing siege support. And with the Barbarian race gaining +100 gold for each enemy building destroyed, the Swamp Dragon simply goes hand in hand with the Barbarians' play style. With the free gold given upon burning down an enemy building and the Barbarians' lack of need for crystal, their Dragon production simply snowballs once a Swamp Dragon hits the field. Even excess gold can be traded for additional crystal if necessary.

The Swamp Dragon is just as useful against infantry as it is against buildings. Its elemental attack helps the Barbarians with type coverage where no other unit available to the race possess a fire type attack - not even their Hero without the Pyromancer or Elementalist Hero classes. Its ability to erode armor is also very effective for the Barbarians as they tend to swarm and thus are more units ready to exploit even a minor armor drop to high effect.

Benefits from Training, Eagle Eye, and Magical Tattoos researches.

Empire
The Swamp Dragon is a great dragon, dealing massive damage against buildings and punishing units by eroding their armor. However, when the Dragons become available for the Empire, they also have access to their Mages, who compete for resources and generally are more useful. To make things even more unsettling for the Swamp Dragon is that among the Mage choices is the Red Mage, an unit who also specializes in dealing fire type damage. Due to the natural synergy between the different Mages, this usually results in the Empire player preferring to spend their resources on them, but more to the point for this case, the Red Mage.

So, although the Swamp Dragon is a great unit, the Empire would prefer to spend their resources on the Red Mage and co for a much more effective strategy. The Swamp Dragon can still be viable to them, but needs to be used in a way that's different to anything the Mages can do, such as taking advantage of the Swamp Dragon's ability to fly and exploiting vulnerable areas in an enemy's base defense with it.

Benefits from Armorer research.

Fey
It looks like the Fey don't praise the Swamp Dragon as much as the other races do. First, by the time dragons are available, the Fey already have the means to swarm a base and destroy buildings. Secondly, although any less armor should be welcomed by so low physical damage dealers as the Sprites, the Sylphs and the Spriggans, all those units do critical effects that ignore armor! The only use for a fire-resistant Swamp Dragon would be then to soak up damage from a fire-dealing titan or dragon. Also, on behalf of Faery Dragons, they may be the Fey's only fire-dealers, allowing to keep non upgraded Pixies for their freezing capability, should the Fey need it.

Nonetheless, for economic reasons, the main production effort should be put into Celestial Dragons, even if a couple of Swarm Dragons wouldn't hurt if affordable.

Benefits from Panoply, Lore, and Eagle Eye researches.

Orcs
The Swamp Dragon is a fantastic Dragon choice, unfortunately, its pretty much the only Dragon choice Orcs get. The Orc race lacks fire damage for dealing with buildings / siege weapons effectively, but the Swamp Dragon fills that gap nicely with its powerful, incinerating, splash attacks. The added bonus of eroding armor can be used to soften enemy Dragons and Titans, making them that much easier to be taken down with the likes of Kobold Snipers, or, if you're feeling bold, Ogres / Giants.

Benefits from Training and Eagle Eye researches.

Plaguelords
Plaguelords aren't particularly short of fire splash attacks, but they certainly wont pass up on the opportunity to produce a Swamp Dragon because of it. Typically, Dragons can be tricky to get a hold of, but more so with Plaguelord than any other race. Because of this, you would be forgiven for not owning one when your resources are demanded else where just to keep you in the game. Fortunately for the Plaguelords, with some clever use of their units, they can achieve near enough everything a Swamp Dragon could do for them. This is mostly down to Eyes of Flames and their ability to cross water, and Hydras / Wyverns spreading fear. Of course, a Swamp Dragon is always a great choice and if you can afford one without crumbling in the process, then go for it.

Ssrathi
The Swamp Dragon is in itself a great unit, unfortunately it is pretty much the only Dragon choice the Ssrathi get and it is yet another fire damage type dealing unit. With Snakepriests and Pterodactyls upgraded, the Ssrathi have all the building destroying units they need, which means the Swamp Dragon's most effective use isn't as appreciated here as it would be in another race. That doesn't mean the Swamp Dragon is useless, for its splash damage that erodes armor can scare away many infantry - driving them away from your Snakepriest platoon or at least weakening them to be picked off by your common units, such as Lizard Riders. Ironically, the Snakepriests that lessen the usefulness of the Swamp Dragon also aid it - with their Cauterize spells they can keep the tougher Ssrathi units fighting fit, allowing creatures like the Swamp Dragon to quickly recover from its injuries and then proceed once more into the enemy ranks.

Benefits from Eagle Eye research.