This build is specifically made for Rengar one shot macro, allowing him to deal the maximum amount of the damage in the shortest amount of time possible. And this is how you do it:
1. Make sure the Rapid Firecannon is fully stacked
2. Use Rengar's ult,then activate Yommu's Ghostblade and Rengar's Q as you're approaching your pray.
3. As you're coming out of the ult and jumping onto your target you should simultaneously use/press: blade of the ruined kings active, hydras active, Rengar's W and Smite