Wyverns

I wrote, "if you have to play against an aggressive race" – what, will the Sylvan Elf wait for the Orcs to build up their Rage? I'm not an expert on them, but I wouldn't. The Sylvan Elf has enough units with high Initiative, and I would focus on a lightning-fast attack while the Orcs have little Rage and are most vulnerable. In this case, the first few turns are in favor of the Sylvan Elf. That's what I meant by "playing defensively," meaning you'll have to go on the offensive only after taking down the Dragons, Dancers, and whoever else is there. Simply wasting turns is irrelevant here.