Riven is a very strong champion with her strong passive and mobility. After the nerf for Riven's ultimate it has slowed the speed of her windslash. You should never snipe with Riven's ultimate because it is slow as ****. With the Black Cleaver changes it gives Riven health, mobility, and damage. Adding with Randuin's and Sprit Visage it makes Riven invicible with good sustain provided by your Bloodthirster and Ravenous Hydra. Once you get your core damage and health items, you literally take 0 damage and deal tons of damage. If the enemy happens to build armour, then building Last Whisper instead of Bloodthirster would be more logical. In conclusion, this build is OP as **** and can be used for Rengar as well in top lane.