Walkthroughs for custom maps.

There are even enough free spaces for 8 heroes so that the AI doesn't deploy its troops.

Sounds plausible. We hide behind the castle, summoning a boat for him beforehand, and wait for him to sail away. Then we take the castle, buy 7 heroes, and block the landing with burrows or heroes. After that, when he reveals the entire map, we put 1 hero in a boat and make sure the AI kills him by moving him close to the shore. Then, a clever explosion!