Welcome in my Zac guide! I am am KopruchKillerr and this is my 2nd guide.
Please comment and if you downvote, please tell me why and I'll try to improve it.

Zac is a melee-based AP Carry/AP Bruiser. His task as a carry is to enter the team fight, burst dow enemy carry/ies and survive.

When to pick Zac?? Good question. Zac works best against classic AP based mid mages like Lux, Nidalee, Orianna and Ziggs. His gap closers will make them raging. He works best if enemy midder doesn't have hard CC.
When not to pick Zac? When you know that your mid enemy is very mobile like you ( LeBlanc, Fizz), when you know that he has hard CC ( Cho'Gath, Kassadin, Malzahar), or when you know he will make you useless ( Morgana, Ryze).

Helpful Pros

• Nice burst damage
• Incredible range with his Elastic Slingshot, so he can gank easily
• Great mobility
• ALL OF HIS SKILLS ARE AOE!!!
• Nice ultimate
• Funny animations :)
• He can resurrect with his passive

Nasty Cons

• His abilities cost health (but he can recover it from blobs)
• Not very high AP ratios
• Requires being in the middle of fight
• Squishy (xD)
• Melee (may cause problems with early farming)

- Great passive, similar to Anivia's. But it also allows him to recower health lost on using skills. It works very well with Guardian Angel

- Your early game source of harrasment. Its AP ratio is only 50%, but it deals (as all Zac's abilities) AOE damage. Use it to harass and last-hit minions when required.

- Important part of your burst. Deals AOE damage equal to percentage of enemy's health. Becomes useful late-game. Spam it in every fight (it has short cooldown).

- Makes Zac channel for a second, dash to selected area and deal nice damage to units around place he landed. It has INCREDIBLE range which increases with every skillpoint put in it. Use it to initiate your harass combo, burst down your enemy and while ganking.

let's bounce - Very helpful ultimate. Makes Zac to jump 4 times, dealing damage each bounce. It has slow and knock-up included. Cast when entering teamfights or fighting 1v1.

Recommended

- Helps in chasing, getting away or kiting. Combined with your Elastic Slingshot and let's bounce will make you able you to escape ANY situation. MUST-BE.

- Good for finishing fleeing enemies, securing kills and countering ultimates like Maximum Dosage. Can be exchanged, but i wouldn't recommend it.

Other viable picks

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Explanation

9x Greater Seal of Armor - Reduces physical damage dealt to you. Zac must be in the middle of the teamfight and these runes help to handle this.

9x Greater Glyph of Magic Resist - Same situation as before.

9x Greater Mark of Magic Penetration - Helps with dealing with enemies' magic resist.

3x Greater Quintessence of Ability Power - Pretty obvious choose for any AP carry.

REALLY needs that extra defense, as our item build lacks it (ofc it is pretty obvious, as it's an AP carry build).

Core items

>> >> >>

I personally buy these items in most games.

Explanation

Sorcerer's Shoes - Gives magic penetration, which increases your damage.
Will of the Ancients - Prevents you from losing health while casting spells. But the passive still works!!
Rylai's Crystal Scepter - Gives you 80 AP and some health that you need much. Slow is also a useful bonus.
Rabadon's Deathcap - Gives 130 AP and increases zour whole AP bz 30%! Must-be for an AP carry.

Explanation

let's bounce >> >> >>

First of all I max Q out for early harrasment. Then i max W, since it deals more damage and bigger range than W, which I max out last. Of course put a point in ultimate whenever possible.

Laning phase

During laning phase just farm, farm and harass your enemy. Kill him or force to recall, and when is not in lane push his turret. Repeat until teamfights start. If you got counterpicked just turret-hug and keep farming in safe zone.

Teamfights

Let your tank enter first. Go in using E, then cast ultimate and spam your Q and W on enemy carries.

Skill combos

Standard harras combo: E onto your enemy, Q, W
Make-a-kill combo: E onto your enemy, W, Q, R, W, W,Q
Finishing move 1: E through wall , W
Finishing move 2: Bounce onto him with R and just use Q and W.

Well, thanks for reading!! I would like also to thank jhoijhoi for this great guide. Vote, comment, and feel free to PW me! I will be updating my guide as often as possibe.

2.04.2012 - Guide has been published. Gonna add Situational items section this week.