This build of shaco is revolved around unsealed spellbook and ability haste.

We're maximizing our boxes for maximal fear, because in S15, full AP shaco support damage is lacking IMO.

Instead, with a full build like this we can achieve over 50% CDR (56.7% with 131 AH to be precise) through ability haste and abuse our enemies with our boxes and plethora of summoner spells.

Firstly, we pick flash and exhaust. This is good for battles in our lane and generally.

With unsealed spellbook, after we use our exhaust, we can gank with either teleport or ignite, depending on situation. This makes our roaming potential much more dangerous, especially in the early game.

Ability haste helps you scale into late game as you will be placing mad amounts of boxes and blinking in and out of the shadows like you're a frontline football player trying to make a touchdown.

Shurelias helps speed up your team and yourself, more support.
So does the banner **** with the 10% current hp damage.
Horizon focus will almost always proc on your boxes for even more vision.

When you get cryptobloom, zhonya, or rabbadon, you're even more of a menace.
Cryptobloom heals in teamfight,
zhonya to break ankles even harder,
and rabbadon to scale your damage.

If you want to push, end with nashor's tooth instead and melt turrets.

Deny your enemy vision using red scanners and vision wards, and ward absolutely everything.

Your zoning ability is giga strong, and your map presence and control over objectives will bring you to victory!