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I started playing the "Dragon Slayers" campaign and struggled for quite some time with the Rust Dragons and the Fabled Dragons. Although, to be honest, I didn't know you could choose, so I always ended up facing the Rust Dragons. In the first mission, I recommend taking Titans and waiting for the "EXPLOSION" to appear in the castle. Pay attention; max out your hero's WISDOM, FIRE MAGIC, AIR MAGIC, and EARTH MAGIC to expert level – you'll need it in the following scenarios, although you might not be able to max them all in 8 levels, but at least upgrade 2 skills and also get Intelligence. As soon as you start playing, head down the leftmost path, pass through, then you'll encounter a garrison, defeat it, and then stay to the right. You'll find a hundred Storm Elementals near a well. Defeat them. Before the final stretch, turn around and fight the Diamond Golems for 3 spellbooks. Simply jump over the garrisons and teleporters, enter the two-way teleporter (I don't remember which one exactly). Before the battle with the Dragons, upgrade your soldiers, then jump to the black market and buy artifacts (literally jump, otherwise there will be a nasty EVENT that takes away a lot of resources). Engage in battle with the Dragons. Save your Warriors; they will all be transferred to the mission with the Rust Dragons. In the mission with the Rust Dragons, gather your army and immediately head west from the castle. In the lower left corner of the map (in this area), free KREIG-HAK with a decent army, and together, go defeat the AI (it won't be easy!). After defeating the AI, the mission becomes trivial! In the mission with the Fabled Dragons, the only difficulty for me was the battle with the Naga Legions. This is where the expert levels in Earth, Fire, and Air magic, as well as Intelligence, will come in handy. In the battle with the Naga Legion, use the following tactic: cast Slow, which, at the expert level in Earth magic, affects everyone for the next few turns. Then, blind them and take them out one group at a time. In the very end, there will be a Legion of Royal Nagas. Use the following tactic: bring the archers to the very barrier. In the battle, buy a supply cart and replenish your mana in the castle. In the battle, the Nagas can only reach you through two paths, from above and below. Block them with a Force Field. Since the field disappears after a turn, you won't have to think about which spell to cast. After defeating the Nagas, enter the teleporter and see a terrible sight: 3 groups of Fabled Dragons, each with a hundred. You can go for the closest one, that is, the one on the far right, but this map has a flaw, so you can attack the leftmost group immediately and complete the map. In the last mission, you have time to prepare, but don't linger too long; the map doesn't have any particular difficulties, except for this: IMPORTANT – don't waste mana unnecessarily; you can only restore it in one city. At the very end, you will face: 100 AZURE DRAGONS. However, if the Dragon is upgraded with Ethereal, you can defeat it. For example, when I played the map, I had 83 Titans, 2 Archangels, and 360 Master Gremlins before the battle. After the battle, 7 Titans remained. Then, go and defeat the last Azure Dragon. By the way, if you complete all the tutorials throughout the campaign, you can put even just one Titan against this dragon: without magic, you will still win. I checked it myself.
P.S. This is the very first campaign that I completed, and I don't find it difficult. The campaign for ADRIAN and CATHERINE is much more difficult (FOR ME).
Added 4 minutes ago
Sorry for the grammatical errors; my computer is glitching a bit