Nzinga

Specialty: Earth Heart
Hitting enemies with an Earth Spell temporarily lowers their Magic Defense by 5(+) and delays their skills by 3(+) seconds. When allies are hit with an Earth Spell, their Luck and Morale are temporary increased by 5(+).'

Duration of Magic Defense lowering effect is ~15 seconds.

Stats
Nzinga begins with a high wisdom stat and +5 Morale and Luck

Default Spells
Magic Arrow, Thorn, Revive, Group Cleanse, Earth Shield, Rock Spike

In-Game Hero Strategy
Wisdom and energy are most important for Nzinga. Casting earth spells to decrease enemy's magic defense and increase own troops' luck and morale is the key for victory.

This means you should focus on a high wisdom stat and use earth spells. The earth spells will deal large amounts of damage due to the high wisdom stat and decrease the speed of enemy troops.