Wave clear pressure, roams, and maximum utility.
Creative tools and rule bending
Swap Summoner Spells while out of combat. Swapping to unique Summoner Spells will increase the rate at which you can make future swaps.
Gain a free stopwatch. Stopwatch has a one time use Stasis active.
Start the game with 6 Minion Dematerializers. Killing minions with the item gives permanent bonus damage vs. that minion type.
+5% Max CDR
+5% Summoner Spell CDR
+5% Item CDR
+22 Ability Power or +13 Attack Damage, Adaptive
Gain cooldown reduction and max cooldown reduction on your ultimate. This is increased further each time you use your ultimate, up to a maximum.
Gain 10% CDR when you reach level 10. Excess CDR becomes AP or AD, Adaptive.
The key to this build is lane pressure and roaming. Spellbook plus Cosmic Insight allows you to keep your Teleport on a short cooldown so you're able to shove lane and roam.
Zhonya's and Zilean's [R] grant numerous chances to minimize positioning mistakes.
Don't upgrade the Stopwatch into a Zhonya's early unless you're playing into an assassin matchup and are dying a lot.
Minion Dematerialzer plays a key role in being able to keep the lane pressure/wave clear up so you're able to leave lane and find ganks or fights with your jungler.
The bonus damage to minions allows you to clear waves in 2 bombs without stragglers being left behind to auto attack.
With Zilean's only damage ability being [Q], he heavily relies on the bonus CDR. The extra bit of Summoner CDR also means more TP pressure and Flash safety.
At level 16 Zilean's [R] is already pretty short. With max Ultimate Hat stacks that puts you at a 24s cooldown [R] heading into the mid game.
With good awareness should you be massively reducing the amount of deaths your team takes.
Transcendence allows you to go Morello's and Lucidity as your only 2 CDR items, while still hitting cap.
It also opens the opportunity to buy Zhonya's if need be, against difficult assassin matchups.