Illaoi & Vayne Synergy
Illaoi Top and Vayne ADC win 52.1% of 1,647 Low Elo games together, +1.0 points vs expected, 2-patch window 26.19-26.20.
Researched on LoL patch 26.20. Tips are written to hold at any rank; stats come from Low Elo ranked games up to patch 26.20.
Why this duo works
Illaoi is strongest when melee teams group into her area at objectives, while Vayne is especially effective at shredding tanks. Together they punish frontliners with Illaoi's area threat and Vayne's sustained max-health damage.
Playing the duo
Leap of Faith (R) creates an extra Tentacle for each enemy champion Illaoi hits, while Silver Bolts (W) gives Vayne percentage max-health true damage on repeated hits.
Illaoi is described as an anti-melee pick that excels in objective fights against heavy melee teams, and Vayne is specifically cited as a tank-killer.
How to play as Illaoi
When the enemy frontline groups at an objective, look for a multi-champion Leap of Faith (R); the tentacles create space for Vayne to hit the exposed front line.
How to play as Vayne
Stay behind Illaoi and keep Silver Bolts (W) on the nearest frontliner instead of diving past her tentacle zone; Illaoi's anti-melee threat can hold that space while you deal sustained damage.
Sources
These notes come from r/summonerschool, checked against the champions' abilities.