Vel'Koz vs Senna Support Matchup
Vel'Koz Support wins 53.0% of 1,486 Low Elo games against Senna Support, +1.3 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 Vel'Koz is favored
Vel'Koz's long-range poke makes Senna's walk-up trades to collect Mist costly, and repeated spell hits add Organic Deconstruction's true damage. A Vel'Koz support player describes keeping a Senna from building more than two Grasp stacks over ten minutes, consistent with Vel'Koz controlling the lane's trade windows.
How to play as Vel'Koz
Use angled Q poke when Senna steps forward to attack or collect Mist, then add spells only when you can safely build toward your passive proc. A Vel'Koz support player describes keeping a Senna from stacking Grasp in lane through those repeated trades.
Vel'Koz can apply Organic Deconstruction with repeated spell hits and deal true damage at three stacks, while Senna must step forward to collect Mist and attack; that makes repeated walk-up trades costly for her.
Senna's range and soul collection encourage her to step forward for attacks, while Vel'Koz can punish her with long-range poke and a three-stack passive proc.
How to play as Senna
Avoid walking up for a short trade while Vel'Koz has his spells available; wait for his poke to be spent before stepping forward to collect Mist or attack. (Unverified: no source confirms this note.)
Sources
These notes come from r/supportlol, checked against the champions' abilities.