Champions, large minions, and large monsters drop soul essence on death. Collecting a soul to become Soul Charged. Your next attack on a champion or structure consumes Soul Charged to deal bonus adaptive damage.
Soul Charged lasts 20s, increased to 300s after collecting 150 soul essence.
Bonus damage: 40 - 80 (+0.25 bonus AD) (+0.2 AP) + soul essence collected.
Champion souls - 6 soul essence.
Monster souls - 2 soul essence.
Minion souls - 4 soul essence.