Heroes are the characters that you influence during the game, monsters are your enemies. Heroes may sometimes control monsters through the use of special abilities. Some classes don't get along with each other and you can't have them in the same kingdom. Adepts and Solarii are an example of this. Your town will be attacked occasionally by wandering bands of monsters.
All scenarios are semi-random by design, so that they can be replayed many times.
For example, if you play 'Hold off the goblins' the objective and many map items will be the same, but the layout and the geography will vary from game to game. In addition, there is a freestyle game editor which will allow you to choose from a number of options such as Starting Force, Enemy Force, Map Style. The computer uses your selections to create a new quest. When a multiplayer game begins the the objective is chosen at that time. The game itself will be symbiotic and as competitive as the players choose to make it.