UPDATE 1/12/2013: (Newer build that provides more instant burst and give you the ability to practically 1v1 any champion in the game. However, you will not be able to really be everywhere and only can focus on a few, but hopefully successful, ganks)

Ok so I've been testing a lot of Evelynn builds and there are alternate builds that could give better results if you need to single-handedly carry the entire team in your backpack. The old build still works don't get me wrong but it doesn't snowball as hard as the recent builds that I've tested. I will list the new build and then give explanations:

Start: same as before
Core: , ,
Late Game: , , , , ,

The Core has changed since I realize that the extra magic pen from the sorc boots provide a lot more damage over the mobility boots. The mobility boots have more utility in that you gank more but if the kills aren't secured, there's no point in having them. The kages lucky pick also provides a little snowball since it is easy to pick up and will pay for itself and evolve into a morellonomicon (which I will discuss later). DFG is the absolute best item on Evelynn since she has so much burst and since people can't see her, they will get killed without even the slightest reaction from your opponent. The time where Evelynn really shines in my opinion is at level 11 since your ultimate gets a lot stronger and your opponents don't have that much magic resist yet. The DFG+ ult + e + q spam will kill even the tankiest of champions in seconds.

The Late game items provide extra magic penetration and AP for more damage and the Zhonyas provides the utility to either dodge skill shots or give you the ability to initiate and blow everything on a single target and then be clear for a few seconds so the heat is off you so you can clean up afterwards. The GA is for extra protection in case those few seconds weren't enough. I really like having both Zhonyas and GA since it gives you almost invincibility in team fights.

Morellonomicon isn't really discussed in a lot of Evelynn guides and are often overlooked but I will go in depth to try to persuade you to get this item. Before, we only have a 34% CDR with the Spirit item but Morellonomicon does essentially the same thing as the Spirit item but better. If you have the 4% from Masteries and 15% from DFG, that should add up to 39% CDR (almost the cap of 40%). This translates to about 36 seconds on your ulti at level 16 and also less than 1 second per Q. This means that you can sometimes have 2 or even 3 ultimates per team fight. Also, at this point, your AP should be around 500-600 and since Q scales 45% of that, you will be doing 350-400 AOE damage with just Q alone every second! And since Q does cost 30 mana/second, the mana regen from Morellonomicon can really benefit you over a long period of time.

This new build provides an extreme amount of burst to single target and multi targets while still providing enough damage to be useful over the course of an entire team fight.


Old Build but still viable if you like to be everywhere and provide an equal amount of help throughout the lanes:

Always start with Machete and Pots. After testing Boots and Cloth Armor, there is no way to clear the jungle without going back to base (this is even with full 9/21/0 or 0/30/0 builds). Also, the single point in Ravage gives that needed attack speed to clear the jungle quickly with the Machete.

Update: It is actually viable to start with Boots 3 now if you are given a lot of help on your blue and plan to just gank and not clear the jungle.

Core:
into , into ,

After you get these, you will have 34% CDR, Regen, and Spell Vamp. Spell Vamp is a stat that a lot of people neglect but scales amazing with your AP. When you hit your ult on 3-4 people, you can go from half health to full and even if they focus you, your Q and E will constantly boost your health back up.

Late-Game:
Offensive Items:
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Defensive Items:
,,

You can build these in whatever order you like given the scenario. If you need to do more AoE, get the RC/VS combo to nuke everyone down with your kit. If you need more single target nuke, get the Gunblade or DFG. Gunblade got a huge buff in S3 now that it can refresh itself really quickly if you keep attacking/spamming your abilities. It also gives all those extra perks of AD, AP, Life Steal, and the almighty Spell Vamp. Get GA if getting focused.