League of Legends Reforged Rune: Lethal Tempo

Basic attacks on-attack against enemy champions grant a stack for 6 seconds, refreshing on subsequent attacks and stacking up to 6 times. Gain [5-16% for Melee | 3.6−8% for Ranged] bonus attack speed for each stack, up to [30−96% for Melee | 21.6−48% for Ranged] at maximum stacks (depending on level), at which you also gain 50 bonus attack range and increase the attack speed cap to 10.

Stacks expire by one every 0.5 seconds when the duration ends.