Instructions:
Go to the Map Editor, copy (Ctrl+C) any object, in the Object Editor select the map editor version and click "Paste".
What can be done:
1) The first GroupBox is for the image. Here you can enter the name of a .def file from the .LOD in the "Picture" field, copy the image of another object (copy and paste icons), or select an image of an object of a specific type and subtype ("Type", "Subtype").
2) There is also an "A part of ground" checkbox. Objects with this flag are placed beneath objects without it. For example, pits, silt on water, etc., have this.
3) Next are "Type" and "Subtype" again. This is the actual object type.
4) The list of terrains that this object can be placed on.
5) The object's passability map. Just like in the MapEditor, but with green squares. Now they have a special meaning. If you want to place one object on top of another, make its entrance (only one cell!) green and you will be able to place it anywhere. Then open the map in H3MapTool and click the "Convert Enters" button.
Finally, click "Copy" and Ctrl+V in the map editor.
You can also save and load objects. There are already several interesting objects in the "Objects" folder.
Notes:
1) Do not change the actual type of objects. Many objects have additional properties; if these aren't found, the game crashes. Instead, change the "Appearance".
2) When changing city images, the map editor continues to display them as cities, but in-game they sometimes look correct.
3) In the Data directory lies "Objects.txt", extracted from H3WOG 3.58 .LOD (it was called "ZEOBJCTS.TXT" or "ZOBJCTS.TXT" there) and cleaned of things I didn't need. When updating the WOG version, a new file can be placed in its stead. Objects1.txt contains several interesting objects added by me. You can add more: Objects2.txt, etc.
4) There is also a "Monsters.txt" file there. You can update it using ERM Help. Each line in it must start with the monster number.