I am a low rank, low elo player. But I saw build guides all using offensive masteries and I wanted to make one showing the power of defensive masteries. I've played riven a but and these masteries really improved my game.

These are the standard riven runes. Cool down ,cause she needs it. AD for the power, and health cause she doesn't have enough.

The meat of this build. The main part of this is Strength of the ages. For simply last hitting a siege minion you get 20 health up to 300. On top of that the extra Heath from veterans scars, the armor and magic resist AND the reduced summoner spells cool down helping alleviate the tp nerf. In offense all your losing is some armor pen, which you make up in items, and fervor which doesn't help riven much at all because she doesn't build attack speed. With these masteries you just get such a cushion without and damage loss at all.

Again your standard riven build. I choose mortal reminder for the extra damage, but if you have an opponent with more health and you're not doing health masteries by all means take lord dorminick

Standard riven again. Build q for engage damage and disengage. E for running away and w last because it doesn't help much in terms of damage.

Flash and tp. With distortion and reduced cooldown you can tp to any lane and have great presence.