Hi, my ingame name right now is MurderousDuck, and this is pretty much my first guide. Don't get me wrong, I know this build is bad, well not that bad, but bad, but thats not the point, the point is this is a perfect build for people who:

1. Love one shots. You will one shot their carries, I guarantee it.
2. Are tired of old Hecarim. This is my main reason to resort to this build.
3. Want to have fun. Who doesn't like trampling their foes right?

The runes are pretty simple, some flat AD Marks, some flat Armor Seals, some flat MR Glyphs and some more flat AD Quints. This gives you enough damage in the early game to clear and still have nice ganks.

Masteries are just straight out assassin, get in, get out. I have taken into consideration swapping Thunderlord's Decree for Stormraider's Surge (which don't get me wrong, works super fine, you can burst someone with E and receive even more damage for those 3 seconds), but I just enjoy the early burst damage of Thunderlord's, it is perfect for snowballing like crazy.

Oh the Items, probably the only reason this build works is because of Statikk Shiv and Rapid Firecannon. The amount of damage you will deal with your E is just outrageous. Since the Energized attack of both Statikk and Cannon are sepperate unique Passives, you will have more damage and range for your E from Cannon, and more damage and clear from Statikk, which will be even greater if you crit (which you will with the full build).
The Infinity Edge is just an obvious item in a build like this, amplify your crit E (be aware the E damage does not crit but the damage from the auto will), amplify your Statikk damage and just gives you more AD.
Youmuu's is there as your only source of penetration and as a replacement for Ghost. Trust me, its enough.
Boots are pretty self explanatory.
Essence Reaver is there to complement the remaining 20% Crit Chance left and to give you that nice CDR and AD so you can assassinate more often.

Max your E for early ganking damage, you will not be tanky so don't count on your Q's sustained damage.
Max your Q after E for obvious reasons and W last because it won't really help you that much.

Smite and Flash, the best you can get. If you want to take Smite and Ghost be my guest but with Youmuu's in the build I don't think it will be that necessary.

Well thats pretty much it, I can't give that much of a detailed guide since this is my first "original" build (I know someone must have done it already, by original I mean a build I thought of and adapted to my playstyle over these weeks), but I hope you enjoy it and now you know everything you need to trample your foes!