Jarvan IV vs Briar Jungle Matchup
Jarvan IV Jungle wins 48.0% of 1,997 Low Elo games against Briar Jungle, +0.2 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.
How to play as Jarvan IV
Use your E-Q engage with teammate follow-up, and save Cataclysm(R) until Briar has spent Chilling Scream(E); otherwise she can end Blood Frenzy and create space before your team finishes the target.
Dragon Strike(Q) plus Demacian Standard(E) gives Jarvan a knockup engage, while Briar can end Blood Frenzy(W) with Chilling Scream(E) and turn the close-range follow-up into a wall stun if terrain is nearby.
Cataclysm(R) traps Briar in close quarters, where Jarvan can keep fighting; Briar's self-healing and E shove give her a way to sustain and create space if he commits alone. (Unverified: no source confirms this note.)
How to play as Briar
Don't chase Jarvan while Dragon Strike(Q) and Demacian Standard(E) are both ready; sidestep the knockup or let him spend the combo, then take the close fight while his engage is down. (Unverified: no source confirms this note.)
Sources
These notes come from r/BriarMains, checked against the champions' abilities.