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Regarding turn management, movement calculation, and terrain effects, there is a good article on hugolka.
New here? I'm Roha — want a quick tour?
Since disputes and misunderstandings regarding the rules sometimes arise between players who have just joined online, I will allow myself to give a small piece of advice:)
If you are just starting to play online, it is worth following the standard rules without changing them.
If you want to make changes to the rules, you need to do this before the game, not during the game itself. Otherwise, you will only get confused and argue.
Imagine if drivers started agreeing on traffic rules while driving?
Here's another very important tip for beginners.
If you haven't had time to transfer some of your hero assistants (so that the main hero can speed up with the fastest unit), and there's a stone or wood mine nearby, you can enter it, leave all unnecessary troops there to guard it, and stay on the fast unit to run faster the next day.
This is done as follows: enter the object, press "space" and leave everyone you don't need until the start of the next turn.

Here's another very important tip for beginners.
If you haven't had time to transfer some of your hero assistants (so that the main hero can move faster with the quickest unit), and there's a mine or a forest nearby, you can enter it, leave all unnecessary troops there to guard it, and stay with the fast unit so that you can run faster the next day.
This is done as follows: enter the object, press "space," and leave everyone you don't need until the start of the next turn.
Hello everyone. I'm a beginner in Heroes 3. But I only played against the computer before and only about 5 times with other people. I don't know any 1v1 strategies. I used to play WarCraft, so I understand that you can't go anywhere without strategies.
Please tell me which castles and heroes are the best in duels. Which castle beats which, and which doesn't. And also, what version is everyone playing now, because I have 3 of them!

I agree with Vitya, but I would add Rampart of Mephala; in my opinion, it deserves it.
Yeah, Mephala with her logo is IMHO cooler than Kir with armor =).