July 20, 2012: Removed Abyssal Mask as suggested by TcelesBHsup
(Notes: My thoughts were, they were going to find out you were there one way or another, but I forgot they can still see the aura when you are in bushes and it can give away a potential gank if noticed.)
July 20, 2012: Fixed Pros/Cons as suggested by AegisDevil

Lore-

Evelynn's origins are shrouded in mystery - a mystery she herself helps to perpetuate. What everyone does know about Evelynn, however, is that she is one of the most skilled assassins in Valoran. It is clear upon first meeting her that she is not quite human. Some theorize that she was cursed with a mild form of fantastical vampirism as a child. Supporters of this theory contend that her ability to sap the very life essence of her opponents on (and off) the Fields of Justice, while still being able to tolerate direct sunlight, would account for this belief. There is some evidence that Evelynn originally came from the Shadow Isles - the mysterious island located northwest of Valoran that is eternally blanketed by a thick, unnatural fog. It is thought that the Shadow Isles are home to countless forms of undead, though no one seems eager to perform the exploration necessary to find out the truth. Evelynn neither confirms nor denies her connection to Shadow Isles.

Pros

Moves VERY fast
Deals loads of damage
Fast Jungle
Great ganks
Always invisible so cannot be detected by sight wards

Cons

Very squishy
Can be detected easy
Vision wards are deadly
Focused first in team fights
VERY HARD TO MASTER

Oracle's Elixir is your best tool! Not only is it good for shutting down a Twitch, Shaco, and Akali but you will also be able to take out counter wards for yourself and teammates.

Don't be afraid of fighting someone with an Oracle's Elixir as it no longer has any effect vs Evelynn, they will see you way before you are in range of the orical's vision.

Jungle Eve works best with these two spells Flash and Smite. Why?
Flash can work in two ways for better, or for even greater. If you find yourself in a tizzy with no where else to go, you can always flash over a wall and prey they do not flash and follow you. You can also use it to secure a kill, Say you are standing in the bush just above bot lane, a blitz stands in your way of a sickly and low mana Graves, but blitz is still a brick wall with full mana and hp, You can ping you are going in, flash over the blitz, and get an easy kill slipping into the bushes to the safety of your Shadow Walk. Well Smite, that should be obvious, take out neutral camps fast, secure Drake and Nashor.

Situation spells

Ghost Only take ghost if you do not own move speed quints and feel like you need to walk through minions to get to your target.

Evelynn is an effective roamer, so playing her in the jungle is the obvious choice. Evelynn is now forever invisible which gives you a major advantage if you see them first, the only thing between you and getting that kill is your item choice and how tacitly you move through the map.

Start off with Boots and Three Health Potion, You CAN do this and still start at Blue Buff. Eve is in no way a tank, HOWEVER with armor Seals you will be able to take hits and still take damage. With a proper leash you should take very little damage.

You will want to finish your jungle then head back to wolfs, you should still have enough HP to kill them for a second time. After defeating the wolf camp go back and pick yourself up a Vampiric Scepter and Cloth Armor then head back into your jungle or gank a pushed lane. You should have all three of your skill which will make ganking easy.

After you clear your jungle or get a kill or two, you should be able to finish off your Wriggle's Lantern and maybe if you are lucky your Mobility Boots. Now you will move as fast as a Fighter jet and hit as hard as a speeding missile.

You should start to roam at this point in the game, only going back into your jungle if you are not getting any kills/assists or if you are grabbing a buff or two.

Your next core item is the Trinity Force, Start off the build with a Sheen its the smart idea seeing as it gives your next auto attack super damage after its been proked. Now go ahead and buy the Phage BUT AVOID BUYING the Zeal at all costs, Just jump into a Tri force if possible. Your Dark Frenzy ability will give you all of the attack speed you need, so go for more damage and utility by buying the Phage.


This is where your build starts to alter from the status quot, If you have not won the game with your universal taunt by now then take a look at there team.
- -
Incoming magic damage is multiplied by a factor based on the unit's magic resistance:
Damage multiplier = 100 / (100 + MR) if MR ≥ 0
Damage multiplier = 2 − 100 / (100 − MR) if MR ≤ 0
Examples:
25 magic resistance → ×0.8 incoming magic damage (20% reduction).
100 magic resistance → ×0.5 incoming magic damage (50% reduction).
−25 magic resistance → ×1.2 incoming magic damage (20% increase).
-
If there team has a lot of magic damage champions such as Akali, Amumu, Karthus, Kassadin, Nidalee, Sona, Soraka, Ziggs Zilean, or Twisted Fate consider building magic resist items such as a Banshee's Veil, or Maw of Malmortius. Remeber Evelynn is a Hybrid champion and she scales off of both AD and AP ratios.
-
I personally end up grabbing the Wit's End for its Unique passive: Physical attacks deal 42 bonus magic damage and increase your magic resistance by 5 for 5 seconds. (stacks up to 4 times).
- -

If there team has champions such as Ashe, Caitlyn, Corki, Draven, Ezreal, Gangplank, Graves, Irelia, Jarvan IV, Sivir, or Varus consider buying health items over armor items. Usually Attack Damage Carry champions build Armor penetration runes and they will still shut you down.
-
The items I usually take are Randuin's Omen or an Aegis of the Legion of the tank or support champions fail to grab one.
- -
Given 20 flat armor reduction and 30% armor reduction, and the target is affected by 10 flat armor penetration and 40% armor penetration,
Target A has 80 armor.
The 80 is reduced to 60 by the 20 armor reduction.
The 60 is reduced to 42 by the 30% armor reduction.
The 42 is considered to be 32 by your 10 armor penetration.
The 32 is considered to be 19.2 by your 40% armor penetration.
Target A takes damage as if it has 19.2 armor.
Target B has 18 armor.
The 18 is reduced to −2 by your 20 armor reduction.
The −2 is not affected by any further calculations because it is less than 0.
Target B takes damage as if it has −2 armor.
-
Armor champions such as Olaf, Rammus or Mordekaiser can spell defeat for a Evelynn player. You will never truly be able to counter them but for the best results consider taking Armor Penetration items. I take Last Whisper or a Black Cleaver depending on how much armor they have all together.
-

End your build with one of two items, Guardian Angel if you find yourself dieing more than you would like, or a Banshee's Veil if they have lots of shut down crowd control abilitys.

Start at blue buff if you have no plans on early ganks. Start at the Elder Golem buff and make sure to ask for a hard leash, use Smite on the golem then move on over to the Wolf camp positioning yourself on the side of a small blue wolf to utilize your Hate Spike skill ( Q ). After you clean up wolfs head over to wraiths, Position yourself in front of the lead wraith and open with an auto attack followed by Hate Spike Make sure to keep yourself positioned to the point where your ( Q ) is hitting most or all of the creeps. After killing the camp head over to the double golem camp skipping red while you wait for Smite to come off of cool down. Position yourself to the side of the small golem opening with an auto attack then quickly change your focus to the larger golem spamming your Hate Spike and Ravage abilitys. Smite should be back up by now so head on over to your Elder lizard buff positioning yourself to the side of the smaller creep, open up with an auto attack followed by Hate Spike and Ravage.
-
Depending on how much damage you took head back to base or go back to the wolf camp and clean them up. Head back to base and buy your Vampiric Scepter and Cloth Armor once returning to battle see if you can get any good ganks in before returning to your jungle.
-

Starting at red on blue team is the best idea, be sure to take Hate Spike as your stating skill and start at wraith camp, You leash and ask for damage to be dealt. Move over to the elder lizard as it spawns and have someone leash and deal damage, quickly clear the camp using Smite to finish off the leader and move down to bot lane. If possible get into the bushes at the bottom of the lane and wait for the support to over extend. After the assumed successful first blood head back into your jungle opening back up with Wraiths, wolfs, then Back. Smite should be back up so head over to blue and continue with your jungle.

On the purple team its not as easy to get to bottom lane. Open up with wraiths leashing them yourself and asking for team to deal damage. Move over to red as soon as possible asking for a leash and heavy damage. Now look out at mid or top lane, if over extended go in for a gank, if not head top and wait in the top most bush. Wait for that leesin to over extend and grab yourself first blood. Head back into your jungle opening back up with wraiths then wolfs then back to base. After head over to your Blue golem as your smite should be back up and continue playing aggressive ganking at any opportunity.