Here's how I did it...
First, I replayed the scenario many times because Laslo would attack as soon as I found the Tear of Ascha. Then, I came up with the idea of making him wander all over the map... he would chase after the Mammoth, then the Horse (sorry for the names – I'm afraid I won't be able to spell them correctly), and as soon as I had one turn left, I would teleport to a city. During this time, I gathered a decent army, but it wasn't enough to kill Laslo... I replayed... I lured Laslo and his companions away from the Mammoth with a feint, and then I sent the Mammoth to attack his cities. I captured two cities at the bottom of the map, and then Laslo realized what was happening and ran back to his former city. Meanwhile, the Mammoth was in the second city, and while Laslo was fighting for his city and settling in, my Mammoth slipped past him and started gathering a huge army... I now had two cities, a human city and a dwarven city, and they were both accumulating troops... Gradually, the Mammoth moved around and gathered resources to buy an army, and then the day came. First, I sent the hero from the human castle to Laslo to see how things were going. I was defeated, but I saw that Laslo hadn't really increased his forces, because he didn't have any mines. I took them all over... and then I sent the Mammoth to attack him and crushed him in one bite – it was almost too easy. I had such a huge army that some of the units didn't even get a chance to fight... but I won decisively!))))