I broke through to the sea at the beginning of the 3rd week, then took back 2 Castles and fought with Archangels.

I wiped out the Finics near the port using 3 Behemoths and 6 goblins. Losses: 6 goblins. This was also somewhere around the third week, judging by the presence of behemoths. It's unlikely anyone had three behemoths on the second week. Brag away—who took them down earlier or what did you use to clear 10 finics? :)

And I cleared the swamp with a second hero (for me, it was Celt) a bit later.
I think the winners used the main hero's retreat and then passed his army to him via a chain of towns for redemption. I just can't figure out how they dealt with Magnus so quickly—meaning, how that battle went.

I cleared the swamp immediately—took the boots and the rusties, but I didn't take back the Fortress there—it would be a pity to give away the hat right away :)
Celt remained my main hero—and he wasn't allowed to retreat :)