While in brush, basic attacking causes Rengar to leap towards his target. Leaping to enter combat generates 1 Ferocity. At 4 Ferocity his next ability is empowered. Casting an empowered ability grants 30 / 40 / 50% (at levels 1 / 7 / 13) bonus movement speed for 1.5 seconds. Whenever a unique champion is killed within 1.5 seconds of taking damage from him, Rengar's attack damage is permanently increased:

1 trophy: +1% bonus attack damage
2 trophies: +4% attack damage
3 trophies: +9% attack damage
4 trophies: +16% attack damage
5 trophies: +25% attack damage