So the obvious question.
"Why would ever do this over a standard Zilean build"

Peel for ranged carries.
Enable melee carries.
Perma CC enemy carries.

Dishing out 99% slows/MS, there is no other champ in the game who can do these things as well as a full CDR Zilean. If you manage to hit "Zilean Mode", you basically play the rest of the match out like a game of chess, deciding which ally gets to zoom in and penta and which enemy has to sit there and watch.

Finally, despite laning phase not being the best, you dish out consisent CC throughout the game and a lot of it is point and click, easy to play.

When I make a build, I like to be very clear on what my champ can and can't do.

ZILEAN DOES NO DAMAGE WITH THIS BUILD. AT ALL

This is what you sacrifice for god-like speed. You will not be able to poke the enemy laners out. Do not assume you can secure a kill if you're low health. You will probably not get an S if that's what you're looking for.

I should also mention on account that you're not building AP, your ultimate will not revive for much (couple hundred HP at best, not over 1K, even mid-late), but it will be on a much lower CD as a result.

Now we're at the important part, so listen up.

ZILEAN MODE: 115 AH + LEVEL 13

If you've been following the build, level 13 is the earliest point you would have W and E maxed. In addition, you should have your support item finished before then, menaing Vigilant Wardstone will unlock. Once that happens AND you're at the point in the build where you have both components to Zeke's completed, you should have precisely 115 AH.

What does this mean?
It means, your W will be on a 2.79s CD. Since your W refreshes your E which lasts 2.5s, you're pretty much able to perma E with a fraction of a second in between. This means in a teamfight, you could let your carry have 2x speed the entire fight or entirely disable an enemy carry (ESPECIALLY if they are melee and have a hard time getting in).
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