
Reviewed for patch 7.3d

Favorable matchup
Reviewed for patch 7.3d
Riven goes in and out of trades with Valor, and Poppy has an ability that stops dashes around her: Steadfast Presence. If it cuts Valor, Riven is slowed and grounded in the worst possible spot, and Heroic Charge can carry her into a wall.
Steadfast Presence gives Poppy movement speed and stops enemy dashes around her; whoever gets stopped is also slowed and grounded. Valor is the short shielded step Riven uses to enter a trade or to leave it.
Steadfast Presence's passive gives her armor and magic resist, and more when she's low on health. Riven wins trades with short bursts of abilities and attacks; against a target that gets tougher as you bring it down, that burst does less.
Heroic Charge dashes to the target and pushes it back; if it hits a wall, it's stunned. Around the tower and at the river entrances there are plenty of walls: when Riven fights right next to one, you have a stun available.
Look for the trade when Riven has to use Valor to go in. With Steadfast Presence ready, every engage of hers is an opportunity; if you spend it without stopping anything, back off until it's back.
If you're Riven, don't open with Valor while Poppy has Steadfast Presence up: wait for her to activate and spend it, then use Valor to go in with Broken Wings, whose third hit knocks back. Fight away from walls so Heroic Charge can't stun you.

Favorable matchup
Reviewed for patch 7.3d
Renekton plays the Riven lane with short trades and the initiative: in with Slice and Dice, stun with Ruthless Predator and out with the second slash. The moment is when Riven has already spent Valor, which is both her shield and her way out.
Ruthless Predator strikes twice and stuns; with over 50 Fury it strikes three times, deals more damage and stuns for longer. A stun at the start of the trade leaves Riven unable to answer with Ki Burst while it lasts.
Slice and Dice dashes and damages everything along the way, and if it hits an enemy you get a second dash. The first one puts you in the trade; the second takes you out before Riven finishes the three Broken Wings hits.
Reign of Anger builds Fury with your attacks, and more when you're low on health; above 50, your abilities are empowered. Come into the trade with Fury stocked and pick what to empower: Ruthless Predator for the long stun, Cull the Meek if you need the healing.
The window opens when Riven has used Valor to poke or to step into the wave: without her shield and with no way out, a short trade with a stun favors you. While she has it, last-hit and build Fury.
As Riven, save Valor for the moment Renekton comes in with Slice and Dice: the shield soaks his burst and lets you answer. Don't take the trade right after he has hit the wave several times, since that's when he arrives with Fury stocked. If he stuns you, don't chase his second dash toward his side.

Execution matters
Reviewed for patch 7.3d
Kennen against Riven comes down to distance. Thundering Shuriken pokes from range and Mark of the Storm stuns on the third ability hit. The condition is not letting her close the gap: if Riven chains Valor and Ki Burst onto Kennen, the lane slips away from him.
Thundering Shuriken damages the first enemy hit. Riven has to walk up to hit you: every shuriken she takes while last-hitting costs her health without a way to answer.
Mark of the Storm stuns anyone you hit three times with abilities. Electrical Surge adds marks with your attacks and when activated: if Riven already carries two when she goes in, the next hit freezes her in the middle of her combo.
Lightning Rush turns you into lightning with bonus movement speed, unable to attack while it lasts. It's your exit when Riven comes in with Valor: you get away and, when you leave that form, you gain attack speed.
The early levels are for poking with Thundering Shuriken. Riven's window comes when she has Valor and Ki Burst at the same time and you don't have Lightning Rush: at that point, back off.
If you're Riven, the lane is decided the moment you arrive: wait for Kennen to use Lightning Rush or miss the shuriken, then go in with Valor and Ki Burst. With two marks on you, don't take a long trade. His ultimate hits whoever is close to him; if he activates it, get out before the third mark lands.