Hello, I'm hazushikatta. I've played mid lane since early Season 2, and I haven't been as excited for a Champion release this much in, well, ever. I main Ahri, another Champion who is extremely strong with Glacial Augment, which explains my attachment to the build.

I sincerely believe that Glacial might be Neeko's best build, so I figured I'd make this guide to give some ideas to those who might want to try it.

I won't go too much into gameplay until later if I update this, I have been playing her on PBE but because I'm from the OCE region, my ping is high (250+) which makes it a pain.

Pros

Tons of self peel and chase potential
Still does insane damage due to Neeko's ratios and base damages
Flexible build paths
Cheap items
Comically easy to land abilities
Very low cooldown item actives
Strong laning phase
45% CDR; the lowest cooldowns you can get without Essence Reaver (please don't build Essence Reaver on Neeko)
56s CD Zhonya's Hourglass, 22s CD Hextech GLP, 49s CD Twin Shadows

Cons

Slightly less damage than full AP Neeko
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The bread and butter of this build. Sorry for the wall of text, but I want to explain all of this.

Inspiration

Glacial Augment

Self peel since Neeko is relatively immobile, as well as making it much easier to land abilities. Neeko's ratios are high and she still hits very hard with this build, and the Glacial build's item paths are also very flexible and strong in lane (eg Lost Chapter).
Perfect Timing - The additional cooldown reduction on Zhonya's Hourglass (15%) is very valuable and of course you don't have to shell out 600g for Stopwatch. It does only contribute a gold value of 250g toward Zhonya's, but it's still worth it. Boots would also be viable but might make you vulnerable early since you won't be able to buy them before around 10 minutes, and Neeko is potentially very susceptible to ganks when her Flash is down.

Minion Dematerializer

Neeko already has good lane control and pushing power, and Dematerializer only compounds that. Future's Market and Biscuit Delivery also viable, I'd put this down to personal preference.

Cosmic Insight

The item cooldown reduction stacks with Perfect Timing and Ingenious Hunter, and the increased CDR cap is excellent. The Summoner Spell cooldown isn't bad either. Time Warp Tonic is a good alternative if you want to have a good chance against strong early laners with Ignite. Neeko doesn't really need Approach Velocity since we're already going to be slowing people more than enough to catch them.

Domination

Cheap Shot/Taste of Blood

Both solid choices. Cheap Shot because of your E and R being able to proc it, you can technically proc Sudden Impact with your W, but that has a much longer cooldown and is far more situational and unreliable. Taste of Blood is good for lane since you don't have any natural sustain. Your choice here doesn't matter too much, the main reason you want Domination is...

Ingenious Hunter

Since this is a Glacial Augment build, item active cooldown reduction is extremely strong - especially this amount of it. See the Pros and Cons section for key item cooldowns with the combination of this and the other runes that affect item cooldowns.

Stat Shards: AP, AP, HP

Pretty self explanatory. Neeko doesn't need the Attack Speed and you get more than enough CDR from your runes and items. Resistances are situational if you really want to be safe against a lane you think you'll do poorly in. The HP starts out as slightly less gold efficient than the resistances, but becomes better at around level 7.

Core Items

Hextech GLP-800, Twin Shadows, Zhonya's Hourglass

Because of the runes used in this build, these three items should be your core purchases, as they all immensely help your survivability and pick potential, being able to be used both offensively and defensively. With these items you'll be at the CDR cap and be doing a lot of damage due to your AP ratios, and they're all rather cheap.
One of the best things about these items is that they have very flexible build paths, with cheap components that offer good benefits - this build has Lost Chapter, Hextech Revolver, two Fiendish Codexes, Aether Wisp, and Seeker's Armguard, all of which are good laning items, and you can easily mix and match to suit the situation and not be very behind in your items.

Other Items

Which of these you'll buy depends on the game, how well you're doing, and how well the enemy team is doing.
Generally, Rabadon's Deathcap will be a good buy when you already have several other AP items, especially if you're snowballing. You can get this before Zhonya's if you're very confident and want to snowball hard.
Void Staff and Morellonomicon are for when the enemy is building MR or has annoying healing (Mundo, Vladimir, Aatrox).
You already hit like a freight train but Spellbinder will make you hit even harder than that during its fully stacked active, especially if you already have a Rabadon's as well.
Luden's Echo offers a lot of damage, but will overcap you on CDR if you already have GLP, Twin Shadows and Zhonya's. Lich Bane is in a similar spot but lets you take towers with ridiculous ease.