DISCUSSIONS on “Rules for online games in HoMM3 and formulas for calculating player rating.”

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I think it should be consistently stated that it is forbidden to take Pandoras, scrolls, artifacts from under the guard, to visit various locations without first visiting the keymaster's tent... and so on, as described in the text.

However, it is not mentioned in the text.

Why, if you buy a level 3 Mulich in the tavern, you can use him for 4 days, but the one who leveled him up to level 3 must dismiss him immediately, and not after those same 4 days?

Because you might have to buy him. In 4 days, you're unlikely to accomplish much with him.

What's wrong with Sir Mulich?

If I were making the rules, he wouldn't be available for purchase at all, and if you get him in prison, you'd have to dismiss him on the same day.

As I understand it, without fulfilling conditions a), b), and c), any owner of a level 4 spell and a Tantrum can use their spells in any battles, except against enemy human heroes. And fulfilling one of these conditions is only necessary for battles against a human opponent, right?

That's correct, but there are also scrolls - you can use them.