Current questions and answers regarding the map editor.

Well, it's like in a campaign, where it seems like there's only one unit, but in reality, there are 7 archers, cavalry, and so on.

You pre-select the unit you want to modify, then on the left panel, you find the "AdditionalStacks" line, and add elements to it (similar to how you prevent creatures from appearing in a city, but this time, you also need to select a creature for each element in the list).
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How do I make it so that when I launch my map, instead of the "Heroes" icon (when you start the developer's scenarios), my own image is displayed? For example, like in Azrail's "Dynasty" map.

This is done through modding; I would recommend doing this as a last step.