Hitting an enemy champion with a basic ability while located at least 600 units away from them at the time of the hit reduces its current cooldown by 80% of its total cooldown, modified to 65% for damage over time abilities.
This augment page for Skilled Sniper reflects public Arena Mayhem data for patch 26.19.
Graded against the other augments of its rarity, from all champions' games. The source publishes no per-champion results for augments.
See the Gold tier list