Which school of magic do you prefer and why?

A clone is just…!!!

:) Even a clone will have 1000 snipers with 1 HP :) Even one peasant (well, I might be exaggerating a bit, but…) can destroy this legion :)
Although, it can also be used for other purposes, for example, to make the enemy hero cast a spell on this unit, thus wasting their turn. But…

Forgetfulness - all enemy ranged units stop shooting and walk (even on the advanced level!!!)

After that, we use:

Dispel - Super!!! The opponent has cursed armor, and they also cast a shield on themselves - we dispel it and destroy them

:)