I just checked FizMiG, and it says the following about unicorns:

With a 20% chance, it blinds the enemy (similar to the Blind spell). It emits a magical aura that grants 20% magic resistance to all its warriors on adjacent tiles.

It says 20% and all adjacent tiles... I don't remember for sure if it's ALL adjacent tiles, but 20% seems a bit high to me. In short, it needs to be tested. If anyone is willing, create a save file where two heroes meet, one with 1 spell point and 3600 mana, and the other with unicorns and another unit that will stand in front, behind, and further away. Let the first hero cast mass slow every round, and in the next round, it will disappear, and so on. Then, just apply what you learned in math class. I think after 100-200 rounds, everything will become clear.