Which units would you replace in the Sylvan castle?

I would have preferred to see pegasi instead of ents; everything else is great.
Regarding the dancing units, I agree with the conservative approach – the dancing with the wind units are indeed stronger than the orcish fighters in terms of stats, and the dancing with death units deal so much damage in large battles that it's better not to watch.
As for the dryads, I don't even know what to say... they could have made some priestesses if there weren't already druids – they are essentially priests.
Dragons shouldn't be weakened or strengthened – 7 crystalline opponents can easily take down a stack of units, and unicorns only exacerbate the situation by finishing off the wounded.