Rules for offline tournaments for Heroes of Might and Magic IV.

Here, they talk about extracting a tomb from under the monsters [...] tell me – what kind of trick is that?

Oh, I'm not very good at explaining.
1. Move a unit onto the tomb, and you'll enter the army dialogue (two rows of slots).
2. Press the spacebar, the unit jumps to the top row, and the tomb goes to the bottom. The spacebar is only needed for this; otherwise, you won't be able to move the unit up.
3. Move the tomb to the top with the mouse, and exit the dialogue. The monsters won't attack; now, the unit and the tomb are together.
4. The unit itself won't be able to move away; you need to click on it with another unit and take the whole group. Or not the whole group, depending on the situation.
-- done. The tomb has been extracted, the task has been completed, let's run to the revival chamber before the corpse starts to stink.

*In step 3, you can change things – don't move the tomb to the top. Then, you can easily extract it from under the first unit with a second unit. However, the first unit will remain stuck and unable to move. But sometimes, that's what you need.

**If you complete step 3, sometimes you can do it without a second unit – enter the dialogue again with the combined army of unit + tomb, and move everyone down. Exit the dialogue. The army will move to the right-up, if there is no obstacle there, or otherwise – to the nearest free direction clockwise from right-up. This method can be used if that direction is suitable.

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Off-topic in response to the signature: Don't mess with my head. Give him metal. At the end of this month, an old man is expected to arrive, who played punk when the word didn't even exist...