Walkthrough tips, Discussion of Campaigns [Heroes 5]

Guys, can you help me out? I'm really getting frustrated... Mission #3 for Inferno (where you have to lead through the elven forests of Agriel)... I can't seem to pass it, even though I'm doing everything right, building what I need and on time, I have a large army, a powerful hero, and I know every corner of the map (I've replayed it about 10 times)... And just when I think I'm about to win, his hero shows up and easily defeats me =((... Please, if anyone has passed it, help me!