Tactics for the Swamp (Fortress).

Based on everything mentioned above, my conclusion is as follows: The Swamp Castle is strong on S maps, and possibly on M maps, but it is unlikely to be able to compete with other castles on XL maps. The strength of the Fortress lies in its rapid development in the early stages, but later on, it falters as others catch up. The creatures do not stand out with their strength (I've written this somewhere before, but I'll repeat it):
Gnoll is a relatively good unit for the first level, but it doesn't quite reach the level of Centaur, Halberdier, and Skeleton (all, of course, upgraded).
Lizard - it's hard to call it a ranged unit. As a unit with ranged attacks, it's not very good... But it's also the only one of its kind in this castle, which complicates the situation.
Dragonfly - good speed, health below average. Also, average attack, defense, and damage. The only thing that stands out is its speed, dispel, and weakness (although a 3-point attack reduction isn't that significant, but it's good for a normal hero). Usually, Dragonflies don't survive more than 2-3 rounds (in battle).
Basilisk - Attack, defense, damage, health, petrification - everything is okay, but the speed is low. By the time it reaches the enemy, the Dragonflies and Wyverns will already be gone. But overall, it's a decent unit.
Gorgon - it has the highest health and defense at its level. BUT, its attack, damage, and especially its speed significantly reduce its combat effectiveness. Deadly gaze is, of course, very good, as it usually deals more damage to creatures of level 7 and above than its regular attack. But if you don't let it get close to creatures of levels 6-7 (which is quite possible, thanks to its speed), it will lose all its usefulness.
Wyvern - well, this is the weakest creature of the 6th tier. Attack, defense, damage, and especially its 70 health are something else. Cyclops, although a ranged unit, is stronger. Poison will be more or less useful if the Wyvern manages to apply it. As with the Dragonfly, it rarely survives to the 3rd round. 15 Death Knights usually defeat 20 Wyverns. This leads to a clear conclusion...
Hydra - everything is average, except for speed. Attacking everyone around is very useful, but due to the aforementioned speed, as with the Basilisk, it won't reach the enemy right away.
As for storming cities with the Swamp Castle, things are (in my opinion) not very good. Dragonflies and Wyverns will fly over the city walls and immediately fall there. If they're lucky, they might apply weakness or poison to someone. The Gnoll, Gorgon, Basilisk, and Hydra will have to walk to the walls and wait for holes to appear. Since heroes of the Fortress usually have poor magic skills, you can't usually rely on earthquake. If the hero has the artillery skill, I think it won't be a problem to destroy the catapult. Then, the main thing is to plug the breached walls with some unit with a decent amount of health and shoot down the unfortunate swamp creatures with archers and magic.
That's how it is... BUT, this is just my opinion. I think I've said everything I wanted to say :) .