Hello MobaFire,
This is my second build and im not the best in English so there will be some grammar mistakes in this build.
In this build, I am going to show you, how to play Dr. Mundo, the most amazing champion is the game!
So why would you even pick Dr. Mundo eeh? Well Dr. Mundo is in some eyes a pretty cool jungler, but he's the best solo top in the entire game. If you like a champion that's a unstoppable killing machine, go and try Dr. Mundo!

*Note: This build is mainly meant for 5v5 Solo-Top but it contains some info for 3v3 and for jungling.
*Another note: This build is aimed at people who have already some expierence
*Yes, another note: If you think that I should improve something tell me, and if you want to dislike why?

It is said that the man now known as Dr. Mundo was born without any sort of conscience. Instead, he had an unquenchable desire to inflict pain through experimentation. By the time he was five, most of the pets in the Zaun neighborhood where Mundo grew up had gone missing. By his teenage years, his parents were nowhere to be found. By the time he had legally acquired his license to practice medicine, he had been acquitted of thirty-eight separate charges of murder by the Zaun authorities; the lack of evidence made prosecution impossible.

Dr. Mundo has become equal parts serial killer and mad scientist, though no one is entirely sure how his butchery qualifies as science. However, he has made tremendous strides in mapping the pain response in the human brain and body, going so far as being able to suppress it, even in the most excruciating of circumstances. He has also tapped into the primal parts of the brain through chemistry, learning how to enhance aggression and adrenaline, as well as dulling conscience and the survival instinct. In short, Dr. Mundo's life's work has been how to create the perfect science-enhanced killer. Unfortunately, the city-state of Noxus regards such behavior as a sign of initiative and ambition, rather than inhumanity. Originally fighting for Zaun, Dr. Mundo was recruited to also fight for Noxus in the League of Legends; the Madman dual faction status represents the fruits of a blossoming relationship between Zaun and Noxus. He continues his experiments to this day, even using himself as an experimental subject, as evidenced by his disfigured appearance and his... unique manner of speaking. There are rumors that the High Command in Noxus has given him free reign to pursue his life's work in his spare time.

Beware the Madman of Zaun. In his eyes, you are already dead.

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Pros: + Has good sustain + He's like a purple Hulk + Has epic harras + Has one of the best quotes + Hard to gank + Strong in an 1v1

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Cons: - Dr. Mundo doesn't like Ignite or other stuff that gives him grievious wound - Not the best in early game - Your Infected Bonesaw can only do their full damage against high HP targets - Some people call Dr. Mundo OP (Is that bad?)

Greater Mark of Magic Penetration: Your main damage comes from your spells, so MP is always nice to have.
Greater Seal of Armor: Extra Armor for the early game, since most solo-tops are AD.
Greater Glyph of Scaling Magic Resist: To give you some erxtra MR in the late-game.
Greater Quintessence of Health: More HP for the early game, not more to say about it.

Alternatives:
Greater Mark of Attack Speed: These are a good choice in the jungle.

Greater Seal of Health: GIMME MOAR HP!!!

Greater Glyph of Magic Resist: Gives more MR in the early, but in the late game less then Greater Glyph of Scaling Magic Resist, and since more solo-tops are AD, Greater Glyph of Scaling Magic Resist is IMO more effective.
Greater Glyph of Health: Since my build that I usealy use has enough MR, I find these actualy pretty nice for the early.

Greater Quintessence of Movement Speed: Movement speed is always good.
Greater Quintessence of Attack Speed: Good for more damage in the jungle.
Greater Quintessence of Spell Vamp: This will let your spells give you HP back instead! (Well not really, but the cost is what... less, you know whatt I mean :P)

*note: If you are a real man, get a full HP rune page >:)

Tanky:DPS:Jungle:

[Mundo's abilities don't use mana, energy or are free. They use your own HP. But will I end up dying just by spamming my cleavers? Haha, your passive will help you in your spammy need and gives good amount of HP back every second. So don't be scared and spam those spells!

Passive: Goes Where He Pleases:
This is just one of da best passives in the entire game. This passive is one of the reasons why Dr. Mundo is the best solo-top and why many Dr. Mundos stack HP. If you follow this build, you will have around the 4000 HP (the cheat sheet doesn't show you the right amount of health), you will regen 0.3 of that, and that's 12 HP. Well you think that doesn't sounds that amazing, but where not talking about that per 5 second **** but about per second. Yeah, does that sound amazing for a passive or what?!

Q: Infected Bonesaw:
This is your bread 'n'butter skill! It's your main damage tool that scales not on your AD or AP, but the enemy's HP, so how healthier the enemy is, how more damage it does. I max this first if im against a champion with ranged harrass or if im being cornered, if not max it second. Tip: with Dr. Mundo you won't need to facecheck, just throw a cleaver in that bush and if you get health back, there is an enemy there (9/10 chance that this won't fail).

W: Heart Zapper:
Helps you farm late game and its good to turn on for a bit more damage in a 1v1 fight. The reduction on slows and stuns, is also a nice to have. I max this last. Tip: don't let it stay on for to long in the early game, because if you do, you will end up backing or dying the whole time.

E: Blunt Force Trauma:
Use it whenever possible to secure your last hits and pushing towers. Also use it whenever you're fighting against enemy champions. I max this out second, but it's to a viable option to max it first if you are against a melee AD, and I get a point early.

R: Maximum Dosage:
This is the most BAWS ult is the entire game! Low health? Press R. Enemy escaping? Press R. Low health enemy is backing under a tower? Press R. etc. Because Dr. Mundo doesn't have mana, you won't need to go back to base, cuz this is a free(well not really free since it costs 20% of your current HP, but it won't cost you any farm) heal, and continue your laning. Level it whenever you can. Oh, it gives to an amazing movement speed bonus :D Tip: DON'T use it whenever the enemy has Ignite in the laning phase, I mean with this don't use your ult, run up to him to kill him, just stay by your tower until Maximum Dosage did his job.

YEAH!!!:
Flash: Always a good choice, since it your: You think you got away, guess what!? and your get free out of jail card.
Teleport: I always take it since you will have an heavy advantage in the laning phase, since you can back to base for your gold to be spend (and HP if really needed), and get back to your lane, maybe missing only 1-2 minions. In my opinion a must for all solo-tops
Exhaust: Always good to have against an AD, and doesn't allow the enemy champion to escape from you.
Ghost: This, combined with Summoner's Wrath if you took it and Maximum Dosage, will grant you some awesome escaping and chasing power. I always take this on a 3v3
Ignite: Good against healers (like yourself, supports and Vladimir) and gives you that extra punch of damage that's needed for that FB.
Smite: You aren't going to pick this on purpose if you want to rock that solo-top, but if you jungle with Dr. Mundo, pick it ofc.

Meh:
Revive: So now you will probably think: Dude, da**** did you smoke? Why the **** will you put Revive in the Meh section? Now, imagine this scenario, you are in some deep **** and you died in that teamfight that's still raging on. Now, because you have Revive you run with that extra movement speed to your team, and guess what? You won that teamfight.
Surge: Well, you could get that FB, and maybe it saves your *** sometimes, but you can get something better then this.
Heal: Pretty good on many other champions, but once you hit lvl 6, you only need it to save your teammates, but not yourself.

What did you smoke...? Can I get some?:
Clairvoyance: Your support should take it. NOT Dr. Mundo!
Clarity: Do i need to really explain why you shouldn't even consider this?
Promote: useless in the laning phase, since you want that farm, not that early tower, because that can let you end up dead since that enemy jungler will take advantage of.
Cleanse: Doesn't remove the 50% healing reduction from a Ignite and you have already an in-build CC reduction system, so in my eyes almost useless.

Starting Items:

: I think that you understand that I like to get HP right? Personal favorite, because you can build it into a Heart of Gold for your Randuin's Omen. Take this only if you took Teleport, or are a skilled Dr. Mundo (->Me), since you won't have any real form of sustain pre-level 6.

+5x : Take this if you feel like that you're against an AD top. Or if you're jungling ofc.

: This gives you some nice all-around stats for the early game. Only thing that's bad on this item that you can't build it in to something.

+3x : This will make you in the early very fast and offers some good sustain with pots. If you are confident in your jungling skills, you can take this too for jungling.

+1x : This gives you great sustain and you can build it into a Warmog's Armor or a Force of Nature.

Core: You want that Heart of Gold for the GP5 and HP boost, Boots ofc. and rush then a Warmog's Armor.

Boots:

: This, + Heart Zapper, will deminish slows and stuns like total bros, COME AT ME CC!

: If the enemy team lacks CC and is more AD then AP get this.

: This combined with Ghost and Maximum Dosage will make you one hell of a speedy mofo.

: 15% cooldown reduction is always nice to have.

: Dr. Mundo's damage is mainly magic, so MP is goof for him.

Optional Items:

: This is a good item, it has all the stats that a good Dr. Mundo needs, but many people think it's a waste of an item slot, and better buy another item. Well what I call this item is the Wriggle's of Dr. Mundos. It gives you that boost that will win you that laning phase. You just sell it if you can get a better item.

: A good item, but many players say: OMG waste of cash, to expensive, you already have that AoE damage from Heart Zapper. Well I say: DOUBLE (insert your stuff here) FOR DOUBLE SUCCES!

: YEAH!!! Because of this badboy you get a T-T-TR-TRIPLE PASSIVE(well actually about 7.8 times your passive xD)! With this you will be a unstoppable killing machine. Fed AP carry? No problem when you have this. Fed AD carry with Madred's Bloodrazor? No problem. And the movement speed bonus is to nice to have.

: HP and your cleavers will slow like hell and Heart Zapper will turn in the constant AoE slow that you always have wished for. But the AP only benefits Heart Zapper and it's not that cost effecient for a Dr. Mundo. Still it's really fun to have it xD

: This is one of my favorite items. You build it out of your Heart of Gold if you bought it. It gives 75 armor, and that's a huge chunk armor that you get. But what I most like about the item is it passive and active. They will slow the carry, in both AS and MS, and let them do less damage to you but too to your team!

: Normally a Ignite will cripple Dr. Mundo. You see this item overhere? Yeah, this badboy removes ALL debuffs, the 50% healing reduction from Ignite included. Are you against a Darius? Ha, this item counter his entire life and make him feel puny like the little **** he is by removing all his stacks from his passive..


: DOUBLE WARMOG'S FOR DOUBLE SUCCES!!!

: This will turn your HP in AD, and you will have ****loads of it so why not?

: An excellent choice for in the jungle and is too a good choice when you at solo-top. IMO somewhat better then Ionic Spark, since it doesn't have to wait for 4 hits to proc. When I get this badboy, If I want to do some jungle creeps, there suddenly gone and I have my cash and buffs. The same with towers, want the push a tower, then *poof* gone. WTF... can somebody explain this.

: IMO this is better then Wit's End for jungling, since you will get some HP and the passive helps better clearing those creep camps.

: After some testing and theory crafting, I think that GA is a great item on Dr. Mundo. BUT you need to have your tanky items, good ol' Triforce, and Wit's End or Ionic Spark, cuz if you don't have damage, the enemy team will just ignore you. When you bought your GA with a Warmog's Armor you will NEVER DIE!!!

: This combined with Randuin's Omen or Rylai's Crystal Scepter won't let anybody escape your path of destruction (except that pesky Master Yi).

: A good item against a fed AP carry, and synergizes well with your Blunt Force Trauma.

The early game will give you, if you(r team) did well, a good mid- and late game. In the early focus on farming. When needed, use you cleavers to farm safe. When you see you can take your enemy, try to zone him. But what if he stays the whole time safe behind his minions? A good question. The best thing is to turn on Blunt Force Trauma and run up to him, I don't mean to really 'attack' him, no, you want to scare him away and walk further from his minions, chase him a bit if it's safe and try to hit a cleaver or two. Repeat this cycle, with friendly, and enemy ganks in the process. After awile it will go for you: good, bad, or sometimes even. After awile it's time for the mid-game.

This is something that I'm always aiming at to work . I try to let them push my first tower and do this (The first minute it goes about the subject, then Siv goes talking about lifestreaming and stuff):
Play Video

In the mid game, farming time is over and you will see that more people are leaving their lane and many times, entire teams go in one lane to push a tower, when the other team responds by going to that lane too to safe that tower. Dr. Mundo is an excellent defender, with his good sustain that let him endure many hits. He can annoy the enemy team with cleavers. If you took Teleport you can use it to push a tower when you see a nearby allied minion wave near. If you have an AS item you would be able to push like a boss and run away when needed with your ult. Always stay with your team so that you can help winning that those team fights (see the teamfights chapter for some 'more' info. You want too to get those drakes and when it's possible, Nashor. Don't forget to buy wards, since it's very important. This will be almost the same in the late-game but the difference is that it really goes more about pushing towers and teamfights.

Start with a Cloth Armor and some pots, and begin with Heart Zapper. I take AS marks, Armor seals, MR per lvl glyphs and the quints is all up to you. You can take two routes.
The Blue route: Wolves >> Blue Buff>> Wraiths >> Red Buff >> Gank if possible, if not do golems.
The Red route: Red Buff >> Gank >> If gank was succesful go back to base, if not go back to jungle when not to low on HP.

Counter Jungling:
I think that Dr. Mundo is a strong counter jungler, and he can easily kite the enemy jungler with cleavers (except Lee Sin). Some people don't like Wriggle's Lantern on Dr. Mundo, but I think that it's a very important item when counter jungling. Use the free wards

*Note: IMO Dr. Mundo is still better in the solo-top since jungle- Dr. Mundo is very poor, and when you don't have good ganks for awile, you need to get cheaper items.

Your role in a teamfight is NOT to initiate, but to first poke the enemy with your cleavers. The one that should initiate a teamfight is a Malphite or Maokai, or a Ashe arrow. If you don't have a good initiator, well you should. If you see that you have 60-70% HP left use our ult. Toggle Heart Zapper and Blunt Force Trauma to do more damage. You can do two things: 1. Protect you AD & AP carry by cleavering every ***** that tries to touch them. 2. You can go on the offence instead and kill their carries.

MORE IS COMING SOON!

Good Teamplay: Always discuss with our team what your next move should be.
Stay Positive: I am meaning with this that you don't yell at your team mates that they are really noob (even if him/her/they are so damn noob, say it once and tell him/her/them what they should do intead), cuz how is calling your team noob winning the game?
Map Awereness: Always keep an eye on the minimap, that is always important!
Kills: If you can, let your AD or AP carry get those kills, in a teamfight you need to focus on getting those kills so you will not really stop attacking someone to give your carry the kill in a teamfight :P (don't chase, if the teamfight is still raging on).
Stay with our team: Always stay with our team in the late-game. If you don't do this, all your teammates will likely die in a teamfight, and that can cost you the game.
Buying Oracle's: Since you're tanky as hell, Oracle's Elixir will give you free gold by killing all the enemy wards without dying in the process.

This is the end of my Dr. Mundo build. I hope you enjoyed my build. Give me some feedback.
And to clear thing up, im NOT a high ELO player, I only got 1200 ELO. I think that this build could be used in ranked play, but I don't know for sure, maybe in low ELO play.

Credits to:
-jhoijhoi for her awesome, helpful guide for how to make a good build and for her template.
-BamUitHetNiets for showing me this awesome champion.
-All the nice people that reviewed my build :D
-SivHD for his baws guide how to play Dr. Mundo:
Play Video /league-of-legends/champion/dr-mundo-26 Play Video

14-06-2012:
-Finished the build.
15-06-2012:
-Added the Greater Seal of Endurance and Greater Quintessence of Endurance on the Runes chapter.
17-06-2012:
-Added the 'Trinity Force?' chapter.
-Added the 'Other items that could be useful' section.
-Added Heal on 'the Summoner Spells' chapter.
22-06-2012:
-Did some little changes on the 'Ability Explenation & Sequence' chapter.
24-06-2012:
-Did some organization work on the 'Items' chapter.
-Swapped the flat HP seals for flat armor seals
-Added Greater Glyph of Cooldown Reduction as an optinial rune choice.
25-06-2012:
-Added the 'Jungling' chapter.
-Added the 'Not really fan of these but...' section.
26-06-2012:
-Changed, and improved the Pro / Cons chapter.
-Improved the 'Item' chapter by adding new items.
-Swapped Phantom Dancer for Trinity Force in the Jungle- Dr. Mundo build.
11-07-2012:
-Added Jungle masteries.
-Added the 'Dr.Mundo V.S ...?' chapter.
13-07-2012:
-Improved the 'Runes' chapter.
-Changed the Jungle build.
-Added the early and mid game chapter.
-Added the Lanefreezing/Laneclogging chapter
-Added Vampiric Scepter to the starting items.
15-07-20212:
-Improved my 'Dr.Mundo V.S ...?' chapter.
19-7-2012:
-Improved the item section.
-Archived the 'Dr. Mundo V.S ...?' chapter
-Changed stuff in the items chapter
20-7-2012:
-Changed the Ability Explenation & Sequence chapter
31-10-2012:
-Removed Trinity Force in the cheat sheet and made it optional, because of the nerf.
1-11-2012:
-TF sucks at Dr. Mundo now.