Hello all, i'm Vlaek and this is my build, i'll be very synthetic and sorry to all if I write in bad english!

First we have to understand why an hybrid build. Why not full AD? Now the skills take AD too! Yes it's true, but AP items give in relation more power to skills than ad items for 2 reasons:
1) 50% from AP and 40% from AD
2) an gives 80 AD that is much less than 140 AP (+30%)of a Other reasons to hybrid build are:
1) Ulti takes only ap
2) With the new and you can slow your enemies at great range!
3) AD is usefull too anyway cuz you have anyway great movement speed to chase your enemies and you take a great amount of attack speed from your .

PROS:
Epic ganks
Great dmg amount
With a well-placed ulti you can shield yourself with more then 1000
Great escape possibilities thanks to W + flash
Epic ganks
Undetectable from minions and sight wards
You can follow without being seen if you stay at the right range

CONS:
Squishy expecially at begin (without your ulti)
Bad sustain in jungle, you need some potions
Oracles and vision wards can give you some problems
She need a new ****ing skin!

These 2 are the only Summoner Spells you can take:

Smite : as all junglers you NEED smite, you need it to do blue and you need it to do red. Evelynn has a bad sustain in jungle so don't think to jungle without smite.

Flash : is the best choice for my opinion, you have a Ghost every 20 sec with your W that breakes all slow effects too, so W + flash is a great combo: 90% safe!

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Exhaust : could be a good choice in place of Flash to do nice ganks, but i'm not so sure, enemies can flash with exhaust and you have less possibilities if you have to run away from a teamfight or a gank. Instead use your red buff smartly!

Ghost: Why ghost? You have dark frenzy (better than ghost!) every 20 sec!

Ignite: NO. You can't use it to jungle, don't gives slows, only the dmg that you DON'T need.

As we said Evelynn is a hybrid jungler, we explained why hybrid is better than ad or only ap.
That's why i chose that strange masteries.
You take AD and AP.
Magic penetration is essential for all your skills, your Lich Bane, Madred's Bloodrazor and the active of Hextech Gunblade.
Armor penetration is not significant, but attack speed yes (!
Havoc give more total dmg, so good for an hybrid!
3% Life steal isn't significant, remember you're hybrid but more ap then ad, so do your counts!

Utility masteries are significants: a good jungler needs the Runic Affinity and a good ganker needs the speed buff!

Remember: you're a jungler! So, what's better than an aoe that hits all your monsters?
Hate spike is the best choice as first skill! Taking a good position you can hit 2 or 3 wolves at each hit and 3 wraiths at 100%!
Hate spike will be your bread and butter, if you use it good you can kite certain enemies as hell, killing them from the distance, i killed an amumu at low levels spamming that while he was chasing me at 100hp! With hate spike you're a nearly-ranged!

The second skill is without any doubts Ravage that does some dmg and gives you attack speed. So usefull when you have the razor cuz gives you more chance to proc when you jungle! With razor or lantern + ravage, you'll clean a jungle very quickly

Take dark frenzy only at lvl 4 and then start to gank as hell! It gives you some passive speed, but the active is soooo usefull! It breakes your slows (exhaust too!) and gives you 30% speed at rank 1, you have a ghost (betther than gost!) every about 20 sec!!

Obviously take ulti when you can.
Agony's Embrace is a great ulti and that's why has also a great cd, if you have blue buff you can drop this ****ing cd and use more often, that's a nice thing!
Use it in teamfights and you'll be a tank! Also good to tower dive when enemies are low on hp. DON'T think to tower dive with a full enemy, you're not a tank! (except you're so fed that with a R+Q+E+Q combo you can shot an enemy, that's happened...)

work in progress