I welcome you all to my Mundo guide. This is also my first guide, so please don't insult unless you give a helpful suggestion. I discovered the wonder that is Mundo at level 18, and I haven't played anyone else since, except for a few tier 5's that I wanted to try. Since then I have combined all my runes into Mundo runes, and got rid of all masteries but Mundo's so as not to confuse me.
I have read some of the other Mundo guides, and none of them seem to be quite like mine. Or, if I may, as good as mine. I hope to enlighten you all with my build, and I sincerely hope you all enjoy it!

*For those of you who are scared of math, it's okay. I did put some math in here, but don't worry, I already did it all for you. Aren't I a nice person? It's just in there for any critics who may say my math is off, and also because I think the stats at 18 are off...

Pros:

Excellent anti-turret ability (One game I took out 5 turrets in 10 minutes without recalling once!)
Amazing late-game health regeneration can keep you alive for a long time
Early-game health regeneration avoids needing to use recall, and still allows you to very effectively harass
Late-game damage is over 200
Over 60% for both resistances in late-game
Great farming ability
In late-game enemies are terrified of you, even if there are 2 of them at full health and only one of you
Fantastic against Baron (solo'd him to less than half health once, without even a full build)

Cons:

Very slow until halfway through mid-game
Slightly lower damage (comparatively) until early late-game
Bad against high DPS carries such as Tryndamere.
Teammates may get mad at you in early-game if you have a bad day and die a lot (in late-game they praise you, though)
Enemies are scared of you late game (you may have read this in pros as well. It's here because , even though it's fun, it makes it hard to get kills late game)

Let's start with runes.
Greater Quintessence of EnduranceMundo has so much health that even a 1% increase is huge. Here's the math for mid-game of an average game: 3651 HP x 1% = 3651 x 0.01 = 36.51 additional HP. Now imagine you have 3 of these quintessences and have 4.5% increased health. For those of you who don't want to do math, here it is: 3651 HP x 4.5% = 3651 x 0.045 = 36.51 x 4.5 = 164.295 additional HP. That's a lot.

Greater Seal of EnduranceLike the Greater Quintessence of Endurance, this provides our Mundo with massive percent health bonuses. Add the 164 HP from the quintessence to the (3651 HP x (0.5% x 9) = 3651 x 4.5% = 3651 x 0.045 = 36.51 x 4.5 = 164.295 HP) 164 HP from the seals and you get 164 + 164 = 328 additional HP. Remember, this is only mid-game.

This is meant to give you greater durability during early-game. When I was only halfway through getting all the runes I had about 4 of these (They're the cheapest tier 3 runes!) and my early-game health was over 750! Here's the math: 3.47 x 9 = 31.23 additional HP at the start of the game. That's quite a lot.

Greater Glyph of VigorThis is probably the least important of the Mundo runes. The problem with finding glyphs for Mundo is that glyphs are focused on mana, not health of damage, and Mundo's lack of mana gets in the way of that. So, I found the best one: Greater Glyph of Vigor. It provides Mundo with a little extra health regeneration, which is really only noticeable during very early-game. But it does get you back in the game faster at the start (See Early-Game Strategy for details).

*Sigh*. Masteries. Hard to explain. The point of this is to get the most health as possible, and when health isn't available, go for health regeneration. Just make sure that when you get the Juggernaut bonus in the defense tree. The extra 3% health is great. Here's the math: 3651 HP x 3% = 3651 x 0.03 = 36.51 x 3 = 109.53 additional HP. Add this to our running total of 328 HP and you have: 328 + 109 = 437. The end. Short and sweet.

Ah, items. Arguably the most important aspect of the gameplay. There are two goals for Mundo's items: health and health regeneration.
Always start with Doran's Shield. This is a good first item because it allows you to get out of base first and get a good position on the field. This is because it is a recommended item, so there is no need to look for it, just click on it at the top of the shop window.
It is important to note for this next part that you don't ever go back to base unless you: a.) haven't already; b.) have less than 35 health; and c.) are over level 2. Only if all of these things are true will you go back to base. Ok, so you died/recalled-because-the-above-applied. You may be asking, "What do I buy now?" That is a good question. You should have over 450 health now, so sell that ******* shield and buy a Ruby Crystal along with, if you have enough, Elixir of Fortitude.
After you die again (at this point you never recall, ever, no exceptions), you are going to buy Regrowth Pendant, or, if you have enough gold, Giant's Belt. From here it is obvious what you are going to do: buy Warmog's Armor.
Now at this point you may be thinking, "Golly Oolab, when are we going to buy boots? It's been (probably) 20 minutes!". Well, guess what? It is still not time to buy boots. Next we are going to get Force of Nature. Start by buying a Regrowth Pendant. Even if you have enough for a Negatron Cloak, don't buy it. Buy 2 Regrowth Pendants before you buy Negatron Cloak. Then, of course, you will buy Force of Nature.
Now comes those boots you were asking about. Contrary to what most of the other Mundo guides say, we will not be getting Mercury's Treads, but rather the cheap, easy, and quick to buy Ninja Tabi. These boots are good for Mundo for several reasons: 1.) Extra speed (duh!); 2.) They reduce damage from basic attacks by 10% (great for going against your weakness: DPS Tryn >:[ !); and 3.) Additional armor, which is not only helpful against DPS's, but balances out your magic resistance and armor levels, since magic resistance was greatly boosted from Force of Nature.
After Ninja Tabi, grab Chain Vest for extra armor, followed by Cloak of Agility just because it says so in the recipe. Obviously, this all leads up to Atma's Impaler, which is in many Mundo guides because it provides attack damage equal to 2% of your maximum health, which is very high, as we have shown already. Here's what 2% looks like: 3651 HP x 2% = 3651 x 0.02 = 36.51 x 2 = 73.02 additional attack damage. Add that to the bonus from Blunt Force Trauma and your normal 70-80-ish damage and you have almost over 300 by end-game.
Following Atma's Impaler, go for the next obvious buy: Spirit Visage. This boost your healing and regeneration effects by 10%, which is a lot (I won't do the math because health regeneration varies so much, but I have gotten it to over +50 health per second, or +250 per 5 seconds, without even using any abilities). Start with a Ruby Crystal, followed soon after by a Kindlegem. From this point you should be able to buy Spirit Visage instantly, but in rare cases (also known as "bad games") you may have to buy Null-Magic Mantle first.
Okay, so you have one slot left. What to do, what to do. Many options here, since the main points are already covered. So, you are going to end this build with another Warmog's Armor, because who doesn't like more health, health regeneration, and attack damage (remember Atma's Impaler) all rolled up into one nice package? Yep, just go for Giant's Belt then run out and tank up enough turrets to buy Warmog's Armor.
It is also important to note that whenever you have enough for an Elixir of Fortitude and not close to enough for your next item, buy it, no matter how late in the game it is. The Elixir of Fortitudes in the item sequence at the beginning are just roughly where I usually buy mine; when I have enough for an elixir but nor for the next recipe item.
Yay! Congratulations! You finished your build!

*for those of you who were too lazy to bother reading the whole thing, here is a short list (in order) of what you are going to buy: Doran's Shield, sell that then buy Ruby Crystal and turn that into Warmog's Armor; Force of Nature; Ninja Tabi; Atma's Impaler; Spirit Visage; Warmog's Armor.

The goal of our first summoner spell, Surge, is to create the perfect turret-killer. Mundo is great at turrets because of his massive health and his E-ability, Blunt Force Trauma. Blunt Force Trauma increases attack damage, and, when combined with Surge's attack speed and Mundo's naturally huge health and health regeneration, he becomes a turret's worst nightmare.
The second summoner ability is used to supplement his health regeneration. Heal is great for negating the health cost of Maximum Dosage and, in early-game, it can even heal beyond what Maximum Dosage cost. It can also be used in combination with Maximum Dosage to escape from DPS Tryndamere. In early-game, it is good for when you and the enemy are low on health, and you know you could kill them with Infected Bonesaw, but you just don't have enough health left to use it, or when you are just plain low on health after the first encounter and just want to refresh yourself.

Skill sequence is probably the second most important part of Mundo. It is important to get the right spells at the right time, or else you won't be able to utilize your items to full extent, or worse, you won't be able to deal enough damage for what level you and the enemy are at.
The first skill to learn is Infected Bonesaw. This will be used to slow and damage an enemy, as well as being able to more easily pick up first blood when they're running from you.
The second skill to learn is Heart Zapper, mainly because it is good for farming. This is necessary fairly early in the game if you want to have a chance at getting Warmog's Armor in time to not suck. The only issue with Heart Zapper at this stage in the game is that it is hard to sustain, so turn it off whenever it is not in full use of 3 or more minions being affected. You can negate some of the cost with Heal, but eventually you have to turn it off. It is also good to get it at level 2 because then, when fighting hand-to-hand with Tryndamere, you can inflict additional damage to him.
The third skill to learn is Blunt Force Trauma because this is around the time when you can destroy a turret, and the extra attack damage is good for this task. It can also be easily and cheaply used against an enemy champion.
After level 3, max Infected Bonesaw immediately, only stopping to pick up Maximum Dosage at level 6 and when you can't get level 5 until you get another skill to level 2 (this new level 2 skill should be Heart Zapper). Then, when Infected Bonesaw is maxed, max-out Heart Zapper, as items can be very expensive, and farming can enable faster leveling, which leads to more skills faster. Only pause this to level up Maximum Dosage again at level 11. After getting level 5 Heart Zapper, go for maxing Blunt Force Trauma, of course, only pausing for maxing Maximum Dosage at level 16.

Thanks for reading this guide. It means a lot to me. This is only part of it, however, and I will be adding strategy and gameplay later. I just wanted to get it out there and get some publicity, if only a little, before the whole thing was finished. Check back later for any updates, and thanks again for reading!