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On the one hand, invisibility is simply amazing when clearing neutral creatures. You can calmly run around with invisible rogues on the battlefield, while the hero leisurely mows down enemy archers. It's almost cheating :) On the other hand, I personally got used to playing with archers; without them, it feels a bit uncomfortable – it's easier to clear slow neutral creatures with archers (in my opinion), and I was very upset that there isn't a single archer in all the dark factions in the alt-upgrade. Although, you can come up with tactics with rogues and heroines... It will be very brutal :rolleyes: But the first level of the elves probably needs to be adjusted. Otherwise, only the low growth rate saves them from being labeled as overpowered.
P.S. Don't be too harsh, because I'm playing Heroes of Might and Magic 5 very little right now, due to working on my diploma and not being able to install Heroes of Might and Magic 5 on my laptop... :( So I might get half of it wrong :o But personally, it seems to me that the upgrades are balanced – no matter what, archers are always useful ;)