The importance of water on the map.

In the final mission of "Blood of the Dragon," you had to cross a small strait to reach the castle. There was also a one-way portal along the way, so the gameplay boiled down to making one trip with a large army, after which you could only receive reinforcements twice. If the castle contained the "Flood Ship" spell, it was, of course, easier, but otherwise, the water became a very serious obstacle.