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Okay, I'll try to help (this is the third time I'm writing a Walkthrough; if I knew who deleted the previous one, I would have...). As far as I remember, the starting position for the Elves is in the lower right corner. The enemies are directly above, on one island; you can only reach it by sailing. Directly to the left, in the corner, is the second island, which can also only be reached by sea. And to the left-up is the third island, which can be reached both by land and underground. (All my advice is oriented as if the map is displayed from bottom to top.)
My hero was developed with Light Magic, without summoning (this has an impact on the Walkthrough).
In the first week, we clear our entire island, except for the passage downwards, WITHOUT any losses.
Then, we buy troops (preferably already having Ents in the Castle), prioritizing Archers, Druids, Ents, and meat in the form of Dryad Dancers; Unicorns can be left. And we go through the Dungeon to capture the middle Castle (we must manage to do this by the end of the week). There is one nuance here: at the start of the mission, a hero with a strong army runs/swims from the left Castle towards us. I distracted him with my left hero in a boat, moving him 3-4 steps in different directions. Thanks to this maneuver, we manage to capture the Inferno and return.
After this, we have two Castles each. And then, the computer either sails from the upper Castle to recapture the Inferno (while we go to his Castle), or attacks us (then we defend the Castle and go to him again).
After capturing this Castle, it usually isn't a problem to finish off the last Castle... Although, the computer from the lower-left corner can recapture the central Castle by sea (the main thing is to buy up the troops in it), but this is no longer a problem, since the main armies have already been destroyed.
Some small tips: try to get at least a couple of Dragons in your army as soon as possible (some of them are very easy to recruit).
And, of course, conduct battles while losing as few troops as possible.
The main forces were Hunters, Druids, Ents, Lords, and meat in the form of Dancer-Dryads, and Dragons.