Tactics for the Swamp (Fortress).

I almost choked... with the upgrade requiring insane resources, they are some of the most expensive at level 6, but the regular ones are fine....

I meant that they can be built right away, and only then will resources be required, but if you build them at the very beginning, they just keep increasing in number (take cyclops, for example!!!!!!, cavalry, unicorns, nagas, montigor!!!! They are all expensive even when you build them. Try to accumulate these resources, and even more so when upgrading wyverns, you need a lot of mercury, but that's not sulfur, which is needed for hydras).