JudasIscariot: Granted, you can put MoM on Impossible and have a challenge
Starmaker: Nope. Pick elves, Life magic. Incarnation, True Sight (spectral warriors can eat your dude when he's still fresh) and Planar Travel (the enchantment, not the single-use Planeshift thing). Dig in for a while, then win.
Well, on 'impossible' the AI gets so much mana it can be a challenge. For example, an AI wizard is casting the Mastery spell and I have to stop them so I kill/banish them. For some reason all their cities revert to neutral and they don't cast Return. (Actually they do, but the game gives no notification, and the spell doesn't exactly work as intended, and I don't find any of this out until later.) And then, some time later,
FROM THE GRAVE they start casting Mastery! Clearly they're not fully dead/banished/whatever, but how do you kill/banish something that's no longer in the physical realm? Going back to when they were still alive and killing them again only has the same result - but I did notice that when I killed them I lost about 16,000 mana... I should have got 1/2 what they had, so they must have had around -32,000 mana. Negative mana? Let's see, the game uses a 16 bit value for mana and, well, the AI's mana cup truly doth runneth over! So, go back to the save right before I killed them, use a hex editor to change their mana to be solidly within the realm of the positive, then kill them again. All is well! I get thousands of mana and they gain the ability to successfully cast Return and not lose all their cities. Win-win!
OK, you're right, that might not be much of a challenge for someone used to debugging and hacking. But I'm sure there's
someone out there that would find that challenging.