Light or Dark magic.

That's just funny.

The attack and defense stats are very helpful for the Academy army. If there is a high chance of switching to light/dark, and resources are scarce, you can switch the Academy hero to a Haven hero, if the development allows. Three ranged units with light and Haven attack and defense deal a lot of damage. The Knight has an easy path to empathy, defense, and attack (retribution + ranged attack).

Out of all the non-native hero-army combinations, this is one of the most viable!