to the above poster, I agree wriggle's is more useful than atma's, but it does NOT give more damage and more armor than atma's. What makes it useful for riven is the lifesteal and the wards. This build is somewhat lacking in bonus damage though. I like the concept (100% splash damage is nice, but not too useful in 1v1 situations), but it might need a little work with the pre-items.

I am going to try Tiamat on Riven, sound like fun dashing into a bunch of ppl doing splash dmg. Alot of assists at least ;) Doing splash AD dmg tells me one thing about survivability: Life steal. You have very little of it in this build and Riven will go down like a sack of potatoes if focused without it. I'd at least switch out the Atma's Impaler as Riven's got very little HP for a melee DPS and does not get much out of this item. Besides, the crit is sort of waste on Riven. Try Wriggler's Lantern instead. Cheaper, more dmg, more armor, 18% life steal and makes it easier to farm. Other than that, I don't really see the use of Frozen Mallet either.. The slow does not help you anything in a teamfight and keeping up with ppl trying to run away is not a big deal with Riven. I'd switch that out for a defensive item; HP, magic resist or armor - depending on the opposite team, and maybe get exchaust instead of ignite for the slow/guaranteed kill. Better for defense as well if needed. Other than that, nice reading :)