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Rampart is one of the most interesting castles for me in terms of tactics. In the early game, focus on archers (elves), then transition to heavy artillery (dragons + unicorns).
Excellent selection of heroes. Kirra is one of the three heroes that are practically overpowered (Kirra, Dessa, and Gunnar) due to the "Logistics" special ability – +5% Logistics per level. Calculate at what level the hero will move twice as far as usual (especially with Expert Logistics)! Fast movement means more battles per turn, more experience, and faster leveling. I also want to mention Genova. Ayvora and Elishar quickly gain Logistics and have a good skill tree.
Regarding the skill tree:
1. Logistics
2. Earth – one of the main combat spells for early development (Slow), main combat spells (Implosion and Resurrect) + Town Portal.
3. Air (Haste, Chain Lightning, Counterspell, Dimension Door, Fly)
4. Wisdom – you can't do without it, but you'll get it by level 6 anyway.
5. Tactics
After that, choose according to your preference – Leadership, Defense, Armor, Intelligence, Luck, Archery (very important, especially for Titans – there are 3 ranged units), Water, and sometimes Magic Resistance and Fire with Berserk can be useful. The rest is useless.
I mainly played duels, 1v1. Map L, difficulty "Battleship", no water, random map, no Diplomacy.
Approximate development scenario:
Day 1. The main hero with centaurs runs along the road (all roads lead somewhere). The first weak hero scouts around the castle, the second waits in the castle for the elf upgrade. We build elves.
Day 2. Elf upgrade. The second weak hero gives the elves to the main hero. He goes scouting, and the main hero moves along the road (only with elves and centaurs).
Further construction: Town Hall, Pegasi, Ents, Unicorns, Stronghold (end of the week). Weak heroes collect resources and scout.
Week 2. We go to the Capitol. The main hero buys back the elves, captures the crystals, and clears the area around the castle.
Week 3. We build dragons. We replace centaurs with unicorns.
Then, upgrade dragons and collect everything useful – Utopias, Pandoras, artifacts.
Approximately like this.