And have you tried dismantling the Pyramid? It can't be used in online play. I never found the 7 days that I heard about on the internet. I even tried searching for it through the walkthrough author. It seems they were playing on King difficulty, but I'm not sure. It seems clear that on the 2nd day, the Beaver is taken out (this is difficult on Impossible, because the Warlock with 3 Gargoyles has to defend against at least 4 Wolves and 15 Goblins), on the 4th, or at the latest the 5th, one Necropolis Castle is taken. On the 5th day, a hero is sent to the Warlock, and the Necropolis takes a 2nd Castle, starting a hunt for its heroes. Then, on the 7th day, the first Warlock Castle is reached (presumably weakly guarded, with unredeemed Dragon(s), and then, through a chain reaction, the other 3 Castles are taken by buying heroes in each captured Castle, and a couple of Warlock heroes that are hanging around nearby.
Although, I think I saw information that the starting Castle was a Barbarian Castle, in which case you can't eliminate the opponent's Beaver on the 2nd day.