This build focuses on the idea of making riven able to deal with anyone on the rift no matter who your team feeds since late game Riven is basically playing URF with her CDR and the two AOE stuns, 3rd q and w, in her kit she can keep the effect of Mask, that the enemy takes 15% more dmg for 5 sec, on the enemy for as long as possible plus the ability to apply it to multiple people, with the addition of ghost witch grants movement speed that allows you to catch up to mages and ADC's you can take anyone out on the rift, with no loss of survivability and the tenacity bonus granted from your runes. Last of all since mask and ghost are so cheap it allows you to hit power spikes faster in the game