Hello. This is what happens when a map isn't tested enough and is just thrown together... I completed it with a large army of creatures, in the late game, using Haven and summoning. The remix, I think, involved mass knights with vampirism, before it was banned. Considering the battle and how far away it is, your army is quite weak...
It's not about that, they just attack at the end of the 3rd month... There is, of course, an idea... But I don't really want to lose the entire army to them, all the griffins, unicorns, and angels, and summoning with 8 spells won't get you very far... So, why did you take the vampire, or do you need to complete the entire map in 4 months? Or should I just give up?