Which units would you replace in the Sylvan castle?

I would replace the Blade Dancers and Death Dancers with Pegasuses.

That's a very valid point, but Pegasuses would be too weak considering their actual capabilities. You just can't give Pegasuses less than 25-30 hit points. : ) They would need to be level 4, or at worst, level 3... But I don't even know what I could replace the Dancers with.