ITEMS TO CONSIDER:
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haven't tried the CDR boots myself. not sure if this build provides sufficient mana regen but if u went with manreg runes this is definitely an option

For summoner spells i go ghost and clarity.
ghost+haste+swiftboots= 612 mov speed!!!
people argue about clarity but honestly if i had to change any spell it would be ghost and NOT clarity. WHY? saves rune space for more early dmg, allows you and your partner to stay in the lane longer, intimidates low health enemies as the dmg you (or you and your partner) are doing is causing themn to fight back/waste mana (let them see you and your partners mana go to full), and finally successful teamfights usually lead to your team wanting to group up and push and theres almost always someone who needs it.

everyones play style is different! everyone needs to find that balance of being able to stay in the lane and do sufficient dmg. the runes and clarity and doran's work VERY VERY well for me. MAY BE DIFFERENT FOR YOU.

Runes & Masteries
I feel like the runes and masteries are self explainitory. Caster masteries and flat bonus ap. (per lvl ap sucks dnt get it. do good early game and late game will be no different)

Spell Sequence
Are you wondering why i get timewarp second instead of rewind? Well you shouldn't. OMG WHY? You have low mana so u cant be spamming bombs and a lot of times you go for a double bomb but cant reach the target for bomb number two after you pop rewind and there goes your mana. So get timewarp 2nd and save rewind for lvl 4. Max out ur bombs then alternate between rewind and timewarp snagging ur ult when u can cause who doesnt?

Items
Doran's is the best first item with these runes. for those who dont like it do the extremely hard math. +30 AP from runes and +10 AP, 120 HP, and 5 mana reg is a hefty start. The reason why i only show these items is because the second to last item is always different for survivability. Frozen heart and bansheeveils are common choices for me since you get survivabilty and mana which adds to your archstaff bonus. If you and your team are dominating get more dmg. (zhonya's, void staff, or if u dnt have enough money for zhonya's, two needlessly large rods.) You can even get another Arch staff. Yes you cant cap twice but you get a %6 bonus instead of %3 and on more mana.
NOTE: sometimes it is smarter to buy two needlessly large rods instead of zhonya's (your poor and its late game and you really need to survive/do more damage). WHY? do the math its more damage for less and if its a really really long gamge u can always sell the 2nd rod to finish off your zhonya's.
Also never leave your base without buying a ward and health pot if u can. cause ull always use them/wish you had them. overall you have to use ur brain. i contradict my survivability items all the time but the ones up top are always in my inv.

Time Bombs
This is gonna be your favorite spell. Very heavy damage and a variety of uses. If a target with a bomb on it dies the bomb will detonate (also bombs detonte preexisting bombs). USE THIS TO YOUR ADVANTAGE. You can place bombs on caster minions to keep melee champs at a distance and punk them out of last hits. Eventually they get tired of this and move in. Pay attention to minion health bars. Why? you can place a bomb on a minion (with last hittable health) near an enemy champ to surprisingly nuke them. You can also place bombs on friendly champions. USE THIS TO YOUR ADVANTAGE. Bomb a friendly rammus, a champ fleeing from a lowhealth enemy champion (due to low mana or cooldowns), intimidate melee champs from targeting a melee partner in lane + farm at the same time, etcetcetcetcetcetc.

Rewind
Introduced at lvl4, this is a very useful spell. Takes 10 seconds off your Q W E R spells. KEEP THAT IN MIND. -10 SEC -10 SEC - 10 SEC... OK!!?? Its also the bread and butter to your dmg combo. Which is Q W Q.

Timewarp
One of my favorite spells of zil's. Give huge movementspeed bonus to allies and huge movementspeed debuff for enemies. You have to keep in mind that you are very squishy. Common tricks include hasting the fed teammate (if its you haste the tank or initiator) into teamfights, slowing a runaway champ, hasting a pursuing teammate into enemy champ, hasting a champ that is in a bad position (USE YOUR BRAIN), and running in and out of tower range to insure a clean bomb placement
hasting in a champion that deals damage to an enemy that later dies counts as an assist

Chronoshift
The reason why teammates love you and enemies hate you. Self explanitory. This spell will take the most practice. sometimes u want enemies to see it and sometimes u dnt. Also keep in mind that in crucial team fights u need to keep your carry alive (strongest link).

important tips for Zilean
when approaching a lategame teamfight it is sometimes wise to timewarp someone in THEN throw a double bomb which includes a rewind which renews your timewarp for retreating or trapping.
if you already popped your ult and theres currently no action, spam ur rewind as much as u can especially when ur shopping as this takes time off ur ult and mana is refunded at spawn IF YOU DIDNT KNOW.
if u happen to get deathfire grasp move it to spot 1 in ur inventory. if ur not using the active then u wasted the money for the item. BE SMART
Be aware of the champs with cc's.


To play zilean correctly use all your spells offensively and defensively. getting 20 stacks on mejais with assists isnt very hard. and you also need to be generous and care about yourteammates. if ur not then think of your ult as a KBD or Killing Blow Denier. Tht way it sounds selfish and you dnt have to listen to QQ's of teammates.


OH YEA!
one might argue that this build has no magic pen. magic pen is mainly for picking off tanks and why would u target the tank? yes casters can get survivabilty but why would u need it for them if your obviously bombing the hell out of baghdad for them to get it so mejais should be fairly stacked. and there 10 mag pen in the runes so unless ur against a team with 4 tanks u shouldnt need it. pick off the weaklings and keep your distance from the tanks and u should be able to get away with no magic pen. i normally do. but if you're really starving for it which does happen,should do the trick


GETTING STARTED

To start off i grab my dorans and one health pot. i then bomb an ally still shopping for being slow =] then i head to the lane to farm my freaking soul away. farm until u have 1470 gold then port back. oneshot your swift boots as it will surprise enemy champs and make it easier for you to harass/stay alive. it also helps to be able to haste an ally to safety without sacrificing yourself. so oneshot them and buy a amplifyingtome and health pot. I know games are unpredictable but you wanna avoid porting back with less than 800gold for your mejais (dnt be afraid to sell it later if youre losing your stacks too much and need survivability more because keeping it will only screw you and your team CLEAN OFF). the rest follows the item sequence for me. ummm tear of goddess before blasting wand...make sure u cap your mana. uhhhmmmm....get familiar with zilean and you'll know how to act late game. But i will say that you should never go alone or be the one to stop a backdooring enemy champion (the missing player in a team fight on the enemy team who assaults an ungaurded tower) unless u have twenty stacks because even super minions can rape zilean LOL. OMG YOU'RE NOT HELPING! STFU! you'll notice that when ur not in teammfights your team's chances of success plunge down. You are a vital player in team fights so the best thing you can do if you want to win is stay with the team (duh..). pay attention to the minimap and any MIA calls. i think thats it...what do u think? and criticism is appreciated. even the negative kind. then again if u got this far it cant be THAT bad......

A shot of a few recent games with zilean and others (and a sneak peak at my AP/tank cho =]. Item seq. is scattered due to arranging potions and wards.