Welcome, welcome to the Carnival of Lulu.
In this guide, I will share with you how I chose to play this Champion within The Crystal Scar.
It might not appeal to everyone, but for some, it just might be wicked enough.
Before I start, I want to mention that I won't overly go in details regarding the functions of The Crystal Scar. I will focus on building Lulu and how to put her skills in effect, according to me.

Yes, yes I know, I am doing it all wrong, and I love it.

BUT lets be fair, so, of course the typical "Cookie Cutter" runes can be used here in place of the Malice runes.
If you insist, you could use greater mark of desolation, Greater Mark of Magic Penetration or even Greater Mark of Attack Speed as you see fit.
To your Glyphs you could also use Greater Glyph of Cooldown Reduction, Greater Glyph of Mana or Greater Glyph of Ability Power.
As for the Seals, well, if you must use a Primary Seal I guess I would advise on Greater Seal of Health.
For the Quintessences, by all means, tickle your desires.

With that said, I'll quickly explain my prime choices.

Within our build we already enjoy the comfort of a decent amount of Cooldown Reduction, we don't need a whole lot of Mana and we're not quite the All-Star Nuker. Oh, and we're definitely NOT gonna build an Infinity Edge.
We are building towards Attack Speed here and nothing has as much synergy with this then Critical Strikes.

So with all that Attack Speed, it gives me tingles to know that I have 20% Critical Strike chance sitting behind me. I feel that it adds well to our oh so tasty concoction.

My choice in Masteries is simple enough, I want to HURT and I do, while being pretty, pretty pesky. I'll mention that I slightly favored Attack Damage over Ability Power as it scales better to our purpose. Its my Guide, and if you don't like it, put your points somewhere else :) If you do feel the need to switch it up, I recommend something involving Swiftness .

We begin our Epic Quest with the fast and diminishing Stinger. I get it first because the money is there. If you like you're boots first, I believe that getting Wealth would solve that. Or you could get two Dagger and Boots instead.
Otherwise get Boots next followed by a Recurve Bow. Finish Kitae's Bloodrazor and your boots of which I chose Mercury's Treads mostly for the Tenacity though the Magic Resist is welcomed.

Now our next item can be played out differently according to game situation. In most cases I'll still go for Zhonya's Hourglass. Seeing as Lulu is tiny and although she has tremendous Crowd Control, it makes her that much harder to kill. In its place I could recommend Rabadon's Deathcap to compliment her skills. Frozen Mallet whom resembles Zhonya's Hourglass's purpose but instead of adding to her skill potency, it addresses her more Crowd Control.

Our next item can also have its counterparts. Wit's End, Ionic Spark or Malady would all do well here depending on what is needed. If your prior item was Rabadon's Deathcap then Malady is commendable. Against a Melee heavy team Ionic Spark would be more useful whereas Wit's End is preferable against a Magic heavy team. Choose wisely!

Finally finish Nashor's Tooth.

If the game drags on I usually get a Giant's Belt that becomes a Frozen Mallet if time permits and if it wasn't bought before. If it was already purchased, fill in with one of the other recommended items such as Ionic Spark, Malady or Zhonya's Hourglass.

Its not finished and I Publish?! Its getting very late but I still feel that the build can be put to use for now, and further explained at a later point. Please let me know how you like playing Lulu in The Crystal Scar using this build. See you soon!