Welcome by my first guide. I've buyed Monkey King, didn't played him that much, but i wanted to show Mobafire how I play him. If you're like this guide, comment what you like about and what i should change if any. If you downvote, leave a comment why you downvoted. Sorry for my bad English if any!

9 Marks of Desolation: Armor Penetration, pretty much straight forward.
9 Seals of Vitality: You want this extra health. This will help early/mid game.
9 Glyphs of Replenishment: This is for early game, so you can spam your skills more before you get Sheen, even after Sheen it's useful.
3 Quintessence: Armor Penetration, same for Marks. Or extra health. They both work.

21/9/0. Pretty much a tanky DPS mastery set. AD + some armor/magic resist.

Good
Exhaust
Flash
Ghost

Viable
Ignite
Teleport
Heal

Really?
Rally
Fortify
Revive
Smite
Cleanse
Clarity
Clairvoyance

I like to start with a Doran's Blade for the extra health and damage, the lifesteal is also nice for extra regen. Then buy Boots and Sapphire Crystal if possible. Then you head back to your lane, gain some gold and go back if you're low on HP or MP. Buy Sheen and buy Berseker Greaves, If you got enough money, buy a Ruby Crystal or/and Long Sword. Later you're making it into a Phage. If you go back again, buy Zeal/Tri-force. Then you want to buy Negatron Cloak. If you don't got enough money for the Banshee's Veil, buy Catalyst. Then Banshee's Veil, Sunfire Cape, Atma's Impaler and Bloodthirster. This build is expensive, but when you got fed, or get lasthits it is nice. Tri-force and Banshee's Veil are your core build.

This is the end of my build :) Hope you gain kills. Remember, if someone is coming into the bush, use Decoy and trick them pretty hard while you just walk away :)

Rate my build and leave comments!