This build is not in depth because I am super lazy. I'm a Plat elo Shaco main. I was fiddling around with some builds when i came across the potency of Runeglaive and Gunblade. These items combined equals explosive results. Let's start with explaining why it's so potent.
Your E and Ult scale beautifully with AP. So runeglaive is pretty good with this. Not to mention the on-hit effect is really gud. 100% of your base AD+30% of your AP for the on-hit effect. That is applified by 20% when attacking from behind. So that by itself is really gud. Now to the gunblade part. Gunblade gives you 40 AD and 80 AP. It also heals you for 12% of all damage deal. But the real reason why we're getting this item is because of it's active. It shoots this little ball of burst that does 150+40% of your AP. PLus it slows for 40%. Gunblade is your 2nd most core item, right next to your runeglaive.
So let's say you're moving behind this poor Zed mid to gank. Make sure you burst him from behind since all your damage is applified by 20% when attacking their ********s. So your combo would be something like this. E first to apply that slow which kicks in the mastery of oppressor letting 2.5% extra damage then Auto attack him. This will be a runglaive auto since you've already Q/E So that applies a nice on-hit effect of 100% base damage+30% of AP PLUS it's a crit as well :) Remember, Guneblade gives you 40 AD plus you have mastery that gives you 10 AD at lvl 18. You should have about roughly 140 AD at lvl 18. After that hit him with the active of your gunblade, dealing 150+40% of your Ap which is a lot. Das a lot of burst yo. He should have a nice good slow on him from E and gunblade active so autoing him will do more since you have Oppressor Mastery :)At the end of all that he should be dead with the help of your fellow ally Mid laner :) Only use your ult defensively or for bait. REMEMBER. The passive of your gunblade heals you for 12% of all damge dealt. That includes Boxes dealing damage and clone exploding on champions. So if you pop ult and walk your clone into 3 champs and they kill it and it blows up dealing like 700 damage, you're gonna get a nice big luxurious heal ^ ^
Also don't try to bait enemies into stacked boxes in a bush. It rarely works, it's a waste of time, and 9/10 times it doesnt work the way you planned it to. Just place 1 box and when enemy walks into it and you think you can kill them immediantly jump on them. You have OPRESSOR MASTERY. You deal 2.5% extra damage on anyone who has impaired movement. That includes Fears. Your boxes fear :) Ludens also works really well with the build too. Its on hit effect combined with all the other things such as runeglaive and gunblade active make for a really nasty burst. Just remember when you Q and auto from behind, it doesnt apply Ludens even though you've used an ability. It will only proc your runeglaive. So use your E to proc your ludens. The passive on it deals damage to 4 others around the target. You're gonna get a small heal from your gunblade passive :)
To top it off you should get Deathcap. It will enhance all of your AP. Then get zhonyas because by then you will be super squishy and be a big target. This build is only for experienced shaco players who are already familiar with him.

If you have any questions or concerns just add me on the NA server. IGN: Shacoh