Tactics for the Swamp (Fortress).

This is a truly strong Castle, and in my opinion, the Gorgon is its main strength. Unfortunately, Hydras are only good for throwing at groups of enemies, but that's still a good use for them.
However, having only one archer is definitely a drawback. Still, with such strong defenses, it's better to focus on melee units.

The Swamp Castle is far from being a strong Castle, THAT'S WHAT I THINK...
Gorgons are indeed powerful (and the only strong unit in this Castle), but they are incredibly slow. They can be effectively countered by units of levels 1-3, and then their main weapon (the witch, or whatever she's called) won't be used against them (she might do something, but losing 10 Pikemen or 10 Archangels makes a big difference). And this witch is also ineffective against Necropolis and Elemental creatures. So, the Death Knight is THE BEST against the Gorgon.
And will the Hydra even reach a group of enemies, let alone survive?
The Gnoll Marauder is not bad, but it can't compete with a Halberdier, let alone a Captain Centaur...
The Lizards are a complete failure; even the Crossbowman is stronger, as he at least does double damage.
The Basilisks are just average and far from being a dream unit.
The Dragonflies (in other versions, Dragonflies) are fast, no doubt, but they usually only get 1-2 hits in before being sent to the afterlife in the swamp.
The Wyverns are the same as the Dragonflies, and you only find a lot of them on Random Maps. In other maps, the Wyvern tree is very rare, so you get about 4 of them per week, just like all the other units. 70 health for a level 6 creature is too little; in one Castle, the health of a level 5 and a level 6 unit is the same. By the way, the Gorgon will be much stronger than the Wyvern.