AnotherGame is a mod for ToE 3.1.

I especially agree with Nargott regarding revenge; it's already been nerfed in 3.1, so why nerf it further? Besides, there are more overpowered spells, like Fan.

I'll revert it when the number of those who disagree exceeds the number of those who agree ;)
Right now, I'm at +3 in favor of keeping it.

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I understand, in Heroes of Might and Magic, most maps have incredibly rich resources due to the huge number of treasure chests. If mines also give double the income...

The main thing is that this is allowed for everyone, and sometimes a single resource is scarce, and an upgrade would be very helpful ;)
Sometimes, players get into trouble when an elf has very few trees scattered around the map, for example ;)