This comp rose to popularity as Riot Mortdog himself tweeted a game where his Yasuo carry beat out ranger players. This is due to Yasuo targeting the champion with the most items, making him an anti meta carry built to assassinate the enemy carries. Be careful with this comp as since Yasuo targets the champion with the most items, players can counter this comp with this knowledge. Elemental hexes count as an item, so a frontline unit with two items and a hex can tank your Yasuo ultimate.
This comp does not require too many core items, but Infinity Edge on Yasuo will be crucial to oneshotting carries. If you have the items to make Blade of the Ruined King, you can also swap out Aatrox for Azir or Kha'Zix for Desert, making this comp even stronger.
In the early game, you mainly want to look for Yasuo and Leona. Any other units will work fine, but Renekton will provide Desert with Sivir later on.
In the midgame, your ideal 6th unit will be a Janna as she will add both cloud and mystic to your team. Karma can tether onto Yasuo for more survivability. If you can't find Janna, a Cloud Qiyana will also be nice, or any transition unit you are able to find will work.
Because this comp is fairly new, it may be uncontested, but if more people play it, more people will contest your units, and other players will itemize accordingly.
If you find Nami, you can replace Soraka for her.
If you are able to find Cloud Lux, you can also swap out 4 mystic for 4 cloud depending on the enemy teams.
Yasuo with GA and HoJ will deal enough damage to nuke carries, and any damage or defensive third item will work too. Sivir should only be itemized if you have extra items, but if you find Blademaster Azir or Kha'Zix, you can prioritize them for items too.
Lastly, if Yasuo 3 is way too far, you can transition out of Yasuo into a Kha'Zix carry build.