I have analyzed the campaign XML files and they're pretty simple. After each scenario units are assigned to a "corpse", which is then specified for the next scenario to use.

I don't have a working editor, but I believe the triggers can't be much more complex. Is it possible to open one of the campaign scenarios and see, how are the triggers set? And more importantly - how are bonuses for silver and gold victories defined, for they are not specified in the campaign XML file, so they have to be in the scenario.

You can set Bonuses for victories in the editor
You must to edit a new trigger that set the starting forces for the next map as the remaining forces you have at the end of the current map

That's good news.

That's not necessary. The campaign engine does it for you. There are entries in the XML file assigning all units to the "corpse" and then indicating, which "corpse" to use for the next scenario. There are also options to turn on/off initial deployment and the "shop" when you upgrade units, buy new ones and distribute artifacts.

I only can't figure out yet, where is the setting for the number of units available. Like in the official campaigns - as the story progresses, you get access to more powerful units.

Is there a way to create a series of maps for multiplayer mode? (aka campaign mode for multiplayer)

I really REALLY want to figure this out... it could lead to some very fun tournaments.

I thought I read here that a campaign editor would be released for this game.

Campaign Editor will be in the next upgraded Editor, actually is still in beta and is not out ( also Russian players are waiting for it ).

I vote for such a feature too! I have been playing two PG2 multiplayer campaigns. They were fun! 4-player scenarios, strategic map... each strategic move resulted in a battle, which was played as a 2, 3, or 4 player scenario with predefined forces. And the forces left after the scenario, together with their newly gained experience, were carried over for future battles. It would be great, if we could play such campaigns in FW. Just imagine - players divided into teams (kingdoms), each having their own division, fighting barony after barony... I want that! :D

Also, I think that there should be (in the sequel) an option to capture artifacts. If an enemy unit has an artifact, and you defeat this unit, you should be able to take that artifact for yourself. What do you think?

<eagerly awaits campaign editor>

cheat codes
 

I've seen cheat codes that say use the ~ or ^ button to open a cheat console...but I can't get it to work...

I've seen cheat codes that say use the ~ or ^ button to open a cheat console...but I can't get it to work...