Walkthrough tips, Discussion of Campaigns [Heroes 5]

Hey guys, can you give me some advice? I'm really getting frustrated... Mission #3 for Inferno (where you have to lead through Agriel's elven forests)... I can't seem to pass it, even though I think I'm doing everything right, building what I need and within the time limit, 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!