Race

Human

Spark of Mind · levels at 3 / 6 different pieces

Humans give courier XP rather than combat stats. XP from Humans can take you past the normal level cap.

3
Gain 2 courier XP at the start of every round.
6
If you win a battle on your own board (creep rounds count) with at least one Human still alive, gain (courier level - 2) XP at the start of the next round.
Note: The tooltip doesn't say that at least one Human must survive the win. Creep round wins also count.

Official in-game tooltip

Species Perk: Spark of Mind
Active when you have at least (N) different human pieces on board. (Multiple effects stack)

(3) Humans: Gain 2 experience points at the start of each round.
(6) Humans: Gain (Courier Level - 2) points of experience points at the start of each round if you won your last home battle.

Humans are an intelligent species that values kindness and cooperation, and silences any who they deem unworthy.