Welcome to my BatSh*t crazy Dr.Mundo guide. This is my way to play Mundo and in this chapter, I will clarify some parts that are deceiving. Most important, that weak health bar, I mean come on 3309 health on Mundo? Well the guide lies when it says Warmog's +350 and 10 Health Regen is included, So Mundo had 3659 health. Thats nice, but not good enough, add the 640 from the Leviathan stacks, now he has 4299 health AND 15% reduced damage. Ok, well now Mundo is tanky enough, what is next, Well what about that Atma? With 4299 health he gains an additional 85.98 damage. So now Mundo has 366.21 damage, pretty damn nice, but when you combine the +40 from Blood Thirster farm, he now does 406.21 damage, when combined with his E gives him 506.21 damage.
Now you know what kind of Madman Mundo is.

Armor Pen Marks are just flat out awesome, nothing needs changing with those.
I leave the Seals up to you, but I prefer the Vitality seals for an awesome Early game boost.
For Glyphs take either Magic Resist or Celerity, these two will benefit your more than anything else.
Armor Pen Quints just enhance your damage Early and Late game. Having 25 armor pen early game means that you will basically be dealing true damage except to the most tanky of early champs.
You can play around with masteries as you please, but this is the most effective combination I've found so far. More gold, more damage, and your harder to kill, whats not to love?

Leviathan, and Sword of the Occult are probably the most controversial item's here.
No matter what, work for those stacks, if you most kill steal, then so be it. When you get max stacks with these two, you become next to unstoppable. Blood Thirster is a fantastic item for Mundo in this build, as it gives him even more sustain for when he isn't using his ult, and with his ult, he might as well be Tryndamere. If you really don't like Blood Thirster, then I would get an item with magic resist, I would choose Wits End.

Poke with your cleaver until they/it is weak enough for the Mundo Charge. In a lane with two, try to of course poke the squishy/carry. When your ready to Charge in, start with your W, and keep throwing cleavers until your in melee range, then activate E. If your about 60% health activate your R. This is standard procedure, if target escapes, repeat until done.
Ghost is for chasing/escaping, while exhaust is for killing/disabling that AD carry.

Pros:
Super high health bar, Cho'Gath will have a problem keeping up with you.
Super high damage, you will keep up with those really annoying damage dealers such as, Tryndamere.
Cons:
Stacks if you cant get involved in fights/kills, then you wont get strong.
Watch out for Rammus, and Nasus.

This build gives you insane damage and health. With baron you have nearly 5k health, and 700 damage when you use your E. 1400 damage crits, show GangPlank whose boss. My Teammates have said that I could probably solo-pentakill, and you can solo baron.
Careful though, your aren't invincible, you are NIGH-Invincible, close, yet so far.

Health: 4.2k
Damage: 600
Move-speed(With 20 stacks) 449
High health, High damage, Mundo hits with the strength of 14 Smart car's. Mundo regenerates health faster than a Hydra can regrow heads