Kayn & Mel Synergy
Kayn Jungle and Mel Support win 45.8% of 1,733 Low Elo games together, +0.7 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
Rhaast gives Mel a reliable setup: Blade's Reach(W) knocks a target up for Solar Snare(E), after which she can build Overwhelm and cash it in with Golden Eclipse(R) from any distance.
Playing the duo
Mel's abilities and attacks apply Overwhelm, and Golden Eclipse(R) can hit marked enemies at any distance, so she can follow Kayn's catch without needing to stay beside him.
How to play as Kayn
When you have Rhaast, land Blade's Reach(W) before Mel fires Solar Snare(E); the knockup gives her a clear center-root follow-up.
In Rhaast form, Blade's Reach(W) also knocks up; Mel's Solar Snare(E) can then root the target at its center.
How to play as Mel
Hold Solar Snare(E) for the moment after Rhaast's W connects so the root follows the knockup instead of overlapping it.
Sources
These notes come from r/MelMains, checked against the champions' abilities.