Gratz!
Though your looses was heavy.
Anyway, most important, you did it
What army was in Necro castle (on hard)?
In impossible enemy had (as i remember) 2 stacks of 1.5k skeleton archers, 2 stacks of 5 bone dragons, 25 necromancers (i was surprised about such weak stack), about 140 old vampires and large stacks of undead spiders and skeletons. Edited: Ahh, remembered, about 180 death knights too.
My army was 4 female and inquisitors (leadership about 17k-18k). I played as mage.