The second option.
A specialist in mines.
When capturing mines, the hero immediately receives a week's worth of mine output.
The third option:
Friendship with death.
When less than 10% of creatures remain on the battlefield, they gain the "ethereal" ability.
(or they receive some free spell, not dependent on the hero's skill in the School of Light magic)
And one more question:
Did Iris (the Griffin Queen for the Order) specifically receive Dark magic at the beginning? Did she have it before?
Or cast a nasty spell and fly away into the heavens.
As I already wrote, there will be 2 versions of the mod, in one of which the standard heroes will also be changed.