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I hope someone still reads this section :)
Yesterday, I learned from my own experience that the effect of the Blind spell differs in Heroes of Might and Magic III and Heroes of Might and Magic II:
1) In Heroes of Might and Magic III, if you attack a blinded unit, it will continue to move during that turn.
2) In Heroes of Might and Magic II, even if you attack a blinded unit, it will no longer move, although it can still retaliate.
Therefore, if you have a lot of mana, some archers (or even towers in a castle), or a unit that doesn't retaliate (vampires, fairies, thieves), you can attack the enemy without consequences by blinding them at the beginning of each turn until your mana runs out.