The idea of the build is to present yourself as a much more lethal threat, one that is more harder to get rid of, one who has over 500 ad / 3000hp / 200 arm / 200 mr yet still retains the armour penetration and reduction of the average Zed.

Some of you may disagree with not using Blade of the Ruined King nor the Ravenous Hydra but I believe the armor and magic resist is well worth the sacrifice.

This build is very effective against magic damage match-ups. By rushing the hexdrinker and then getting the mercurial treads along with the mercurial scimitar and finally building into the maw of malmortius you are almost guaranteed to be "immune" to their ap carries.

By also using Mercurial scimitar you also avoid sticky situations such as opponents with crowd control abilities that can shut you down and let their team murder you.

You may disagree with the "Tank-ier" idea of Zed since assassins are meant to kill their target and slip away...but why not also have some tankier stats with almost the similar damage an average Zed would yield (unincluding the actives), this will allow you to peel for your carry and have a greater influence in a teamfight.

You may be unfimiliar to non-lifesteal items on Zed and that has always been a problem, but in terms of a teamfight how much lifesteal do you plan to proc when you don't want to entirely auto-attack enemies and instead quickly use skills and slip away safely.

This build works well when the majority of the enemy team is of magic damage, this works because Mercurial Scimitar and the Maw of Malmortius are so effective as individual items but together it is like god wanted physical damage carries to smite magic damage carries (although the same can be said by stacking zhonyas hourglass).