Garen vs Riven Top Matchup
Garen Top wins 55.3% of 1,993 Low Elo games against Riven Top, +1.2 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.
Why Garen is favored
Riven can use Valor(E) to absorb Decisive Strike(Q) and disengage, but brief trades often do not stick because Garen can back off and restore lost health through Perseverance(P). Matchup discussions describe even-health trades as favoring Garen for that reason, giving him a repeatable lane edge unless Riven finds a clean all-in or a larger lead.
Measured in High Elo: Garen wins 2.7pp more often than expected over 1,104 games.
How to play as Garen
Use Courage(W) as Riven commits her stun and burst, then wait out Valor(E)'s shield before spending your full trade; do not run into her stun while your defensive window is down.
Courage(W) gives Garen a brief shield and tenacity, which can reduce the impact of Riven's short crowd-control and burst window.
After Garen avoids damage long enough, Perseverance(P) restores health lost in a trade; Riven's Valor(E) can shield an exchange but does not give her the same recovery afterward.
How to play as Riven
Save Valor(E) to shield or dodge Garen's Decisive Strike(Q), and look for a short trade after Garen has used Courage(W); do not spend your shield just to start the fight.
Valor(E) gives Riven a shield and dash, letting her reposition while absorbing some of Garen's Decisive Strike(Q) damage.
Sources
These notes come from r/Rivenmains, checked against the champions' abilities.