The random map must be reviewed by 3rd person because some maps cannot play such as two castles are located together,
There are a lot of tricks.
when his main hero appear close to castle, if you have enough money, you can lighting him or ice-hit him then retreat or surround until kills all units he bring. Then, kill him, get all artifical from him! And he loses a important main hero which he took time and money to train. :)
Other trick like flying, build another castle, learning magic from AI's castle and so on.
One game takes 2-3 hours.