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 [6% for Melee | 4% for Ranged] bonus attack speed for each stack, up to [30% for Melee | 24% for Ranged] at maximum stacks. At max stacks, attacks also fire a note that deals [9-30 for Melee | 6-24 for Ranged], increased by 1% per 1% bonus attack speed, as bonus adaptive damage.

Lethal Tempo also tracks how many of your attacks against champions are Perfectly Timed (Perfectly Timed: Attacks launched within 0.25 seconds of when your attack is ready after previously attacking a champion).

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