I have copied this build because I had an instant downvote by somebody who didnt even read the full build. Please read the entire build or at least try it out before voting. I have sent an in game message or email to all of those that commented on my guide previously. First of all I have been asked many times to make a build for Mundo. This build is for people who can hold out till late game and then want to be able to win the game for your team at that time. It takes a bit to get into the swing of things but once you do you can demolish many people at once late game. I STRESS MUNDO IS NOT AN EARLY CHARACTER. Sorry for no pictures I do not know how to put them in yet. Please comment with the harshest criticism possible. Please actually try this out before voting because if you can follow it you WILL do well

Pros

Amazing late game
Extremely Durable
Extremely High Damage for Tank
Great farmer past lvl 6
Great at Chasing/Escaping

Cons

Ignite Hurts Until you are fully built
Squishy Early game
Not great until you get Atmas
Low attack speed (sometimes its that last hit that kills you)

Start with a ruby crystal it gives you hp regen because of your passive and lets you take much more damage before dieing. My main build is shown
Spirit Visage=>Boots=>Warmogs=>Atmas=>2 defensive items of you choice=> Warmogs armor (sell spirit visage)=> all pots
Yes I do sell spirit visage at the end. I checked the numbers and overall warmogs gives you about 40 more hp regen and 1100 more hp (which gives you about 25 extra damage). You can either get that or another defensive item in exchange for it but the small amount of resistance that it would give you because of diminishing returns is small and overall does not give you as much survivability as the hp and regen does.

It all depends on who you are fighting
If you are Fighting mainly physical -Ninja Tabi=> Thornmail =>Randuins Omen/Warmogs
If you are Fighting mainly Magic - Mercury Treads=> Force of Nature=>Banshees veil
For a Mixed team - Mercury =>Gaurdian angel=>Aegis of the Legion/Warmogs

Here is the order in which you max your abils

1. Ultimate
2. Cleaver
3. Masochism
4. Burning Agony (with 1 pt at lvl 4)

Infected Cleaver - This is your favorite spell, the jack of all trades. You can use it to harass, last hit minions, get that last hit when you cant see someone, or slow someone down when your chasing them or running away. It also does tons of base damage.

Burning Agony - It does ok dmg at the cost of your health. Its uses are AoE farming, CC reduction, Dmg vs non-tanks. The reason I say non tanks is because if somebody has 60% or more magic dmg reduction (minus that 15% pen you have) its dealing more damage to you then them. This wont happen till later in the game though.

Masochism - At a small cost of hp it gives you some of the highest base damage in the game. Use this at all times when your auto attacking, there is no reason not to use this.

Sadism - This is my personal favorite ult in the game. Use this to run away, right before you start getting targeted in a team fight, and to regen hp to stay in a lane, or even to chase because of the movespeed increase. Use this right before or right when people start to target your for best potential.

hp/lvl quints - About 150 extra hp at 18, HELL YAH

Armor pen marks - Much of Mundo's dmg is from his autoattack because of Masochism this just helps you that much more because you do not get any armor pen items through out the game.

Flat Dodge or Magic Resist Seals - Whatever you normally have more trouble with as Mundo should be what you use. Personally I use Dodge because the magic resist doesnt do much late game because of the diminishing returns.

CD glyphs - I cannot stress how much these help you. They bridge that small gap between masochims, let you spam cleaver more, and let you get ult sooner

I go the average 9-21-0 build getting Archaic Knowledge, Deadliness, and Cripple. You get Archaic Knowledge because your cleaver and burning agony do roughly 35% of your damage.
You can also go 0-21-9 for the extra xp and hp regen but I definately prefer going into offence for the magic pen/cd reduction.

Early game (1-9) - Last hit with your cleaver and masochism, dont go for a kill unless you know where everyone is and you are sure you can handle that person, dont use burning agony unless you have more percentage of hp then your opponent or you can get more than 2 lasthits with it almost instantly (it has a very short time before it deals iniital dmg). You are also a viable top/mid if your team does not have any other good options. Dont go back unless you are below 25% hp (at 50 percent start letting them push towards your tower) until you have enough gold for spirit visage and rank 1 boots. Use your ult if you have to to get that extra gold. After that try to stay following the same rules but for tier 2 boots and giants belt. YOU ARE WEAK TO GANKS BEFORE YOU GET RANK 2 BOOTS AFTER SPIRIT VISAGE DONT OVEREXTEND AT THAT TIME, THAT IS WHERE I HAVE GOTTEN MOST OF MY DEATHS.

Mid game (10-16) - Once you hit lvl 9 you should have your cleaver maxed and this is when you start getting good. ALWAYS BE FARMING MINIONS, whether from afar with your cleaver if your afraid of the gank (which you shouldnt be unless they have extremely speedy champs with a disable mia) or being out harassed or you can do it up close with all your abilities to ensure maximum gold. You are fairly durable right now but you are weak to stuns. Get warmogs right when you have enough gold for it so you can start stacking it up.

Late game - Once you finish your build you should be able to 1v1 any champion and even 1v2 some people. You are the true tank of your team even though you can still put out devastation crits (my highest has been around 700 with full tanky build except atmas) and your cleaver does high damage. If you can be the only person to survive a teamfight with an ace you can get rid of a tower or two while the enemy team respawns with no chance of death. If you follow this guide right and your team does not suck you will most likely win the game.

Mundo can kite people like a boss. Just keep spamming your cleaver behind you use burning agony if they get in stun range (use ghost if you have to and you have it up) and if they are at low hp when your ult comes up (which it has many times for me) you can pop it, let you hp regen a little, and go back and kill them if they are low and arent completely able to nuke you down instantly. (which they dont unless they are fed).

Personally I feel that the best laning mate for Mundo is anybody good at harassing, and if they have a disable even better. If your opponent is harassed to low and you let him push you can easily ghost, exaust and finish them off with your cleaver and autoattack.

In ranked I have an 81% win ratio with a K/D/A of 4.5/4.2/10.7 which isnt amazing but its getting better as I play more. Give me your success with this build (even with a side comment) and Ill post the comment and success right here. I will choose 5 at a time that I feel best fit it