Interestingly, on the fixed maps, the Swamp was one of the weakest castles, alongside the Stronghold. It had decent units (mages and warriors) and relatively tough creatures. But it was easily defeated. Here's the statistics from tournaments in St. Petersburg and Michurinsk from 2000-2003. Up to level 6, everyone built all the cities and castles. By the 2nd or 3rd week, a level 6 stack was quite effective, but wyverns were very weak, and hives were rare on most maps. The first turn in battle was crucial. For most castles, the strongest unit was also the fastest, but the Swamp's fast snakes died very quickly. And the hydra was useless... I can't remember any battles where it dominated like a dragon or a behemoth. It took quite a few random tournaments for the Swamp to show its strength. At first, most players focused on wyverns, as it was very tempting to get two level 6 units on the 2nd turn. Only later did players from Moscow show how quickly a herd of cows could become dominant.