I'm tired. There will be explanations when i wake up, but i really don't agree with any jungle mundo builds on here, so be patient and you'll have one in a bit. With pretty colors and pictures and sarcasm you can choke on. I'll go into detail about everything when i actually go into this guide enough. FOR NOW, i give you builds, which i promise do more damage and will have you tanking more than the rest of the builds on here.

Anyways, Dr. Mundo is great champ regardless of having the fastest jungle clear times in the game. Because 9/10 of times you can't defend against his damage output. He has his own CC reduction, does big magic and physical damage that out DPS's most other champs and does % based damage. On top of all that, he is one of the best tanks in the game. So let's begin looking into Dr. Mundo jangle.

PROS

Super tanky
Deals hella deeps
AD steroid
Fastest jungle clears
Great at invading/stealing

CONS

First jungle clear can be scary
Will be targeted by every healing debuff

Adrenaline Rush
It's a passive. It's not great until you get mid-late game. Or you get items that increase how much you heal for.

Infected Cleaver
Most melee champs get kited. Mundo, however, does not because of this. It's a skill shot that does some pretty good magic damage and slows pretty well for how low of a cooldown it's on. If you can land the first cleaver on an enemy, that dollars to donuts they won't be able to run away after.

Burning Agony
Outside of his ultimate, this is Mundo's tanking ability. It reduces the duration of all CC and deals up to 100 magic damage per second. However, it does burn health when you use it. So you do need cloth+5 to jungle with him early, but once you're level 6 potions and lifesteal become useless. I should also mention that this ability, NOT Infected Bonesaw or Blunt Force Trauma increases his jungle speed. Maxing this, before all your other abilities gives you reliable damage output and CC reduction and faster jungle clears/creep farming.

Masochism
This is an attack damage steroid based on how much health you are missing. If you are laning as Mundo, then this is what you take first, and walk into lane and being trading immediately and get FB by yourself because the damage is unexpected and as it drags on, you deal more damage. HOWEVER, you're not laning, you're jungling. So if you're going for full tank or dealing heavy magic damage, you max this last. But if you want an AD heavy Mundo, then max this after Heart Zapper.

Sadism
This makes Dr. Mundo, Dr. ****ing-Mundo. Low on health in the jungle? MUNDO! Need to engage with a movement speed bonus? MUNDO! Need to tank dragon/baron/whole enemy team? MUNDO! This heals for % of your maximum health, so getting a lot of health helps this heal for more as well as your passive. It's also on a pretty low cooldown so don't be afraid to use it in the jungle or trying to engage a gank.

Options for MARKS
For AD Mundo - greater mark of desolation - So your auto attacks do more, derp.
For Standard Mundo - Greater Mark of Magic Penetration - The majority of your abilities and damage is magic damage. Check it in the post-game lobby. It's better than armor pen.
For no damage - Greater Mark of Attack Speed <-- doesn't increase jungle speed by much anyways. Rather useless.

SEALS
Greater Seal of Armor - Only acceptable option for seals. Unless you have flat armor quints, then you can get creative. In which case, i suggest grabbing either greater seal of endurance, greater seal of vitality or greater seal of vigor. Take your pick, they're all viable as long as you have armor quints.

Options for GLYPHS
Greater Glyph of Scaling Magic Resist - Standard for most junglers. However, i could also accept using Greater Glyph of Scaling Cooldown Reduction or Greater Glyph of Cooldown Reduction. Not because It's good on Q, W, or E. But getting extra CD on that ult means you have it up basically once the heal duration ends. It's rather annoying to be against.

Options for QUINTS
For Standard AND AD Mundo - Greater Quintessence of Movement Speed - Don't need extra health, really. Don't need armor pen. Why not make sure you're staying on top of their carries? It's a great way to go, trust me. Not to mention if you're going AD Mundo, then this ensures you are not going to be kited around all day and never deal any damage.
For All Around Damage Output - greater quintessence of desolation - Because you're running Greater Mark of Magic Penetration with these, it ensures that the massive damage you do with Infected Bonesaw and Heart Zapper with actually do something, and your steroid-boosted auto attacks will do something as well with some armor pen. But still, he deals a lot more magic damage than physical.

IMPORTANT MASTERY POINTS

Summoner's Wrath
Improved Exhaust is real stronk. You should get it because if you are counter jungling and get caught by their jungler, you can usually kill them pretty quickly before other lanes can react if you have Exhaust up.

Veteran's Scars
Your everything is based off of health. You use health for abilities, you scale off of max health. If you don't get this in your Mundo masteries, you're doing something very wrong.

Juggernaut
3% extra health. Again, you want as much health as possible, 3% of a Warmog's Armor is actually quite a lot of bonus health you get from this mastery point. Not to mention the 10% extra CC reduction combined with Heart Zapper is like never being CC'ed at all.

Suggested Summoner Spells

Exhaust - You immediately out trade their jungler once this is on them, and can help with ganks. It's too good to pass up in my opinion.
Smite - Because you're jungling. Steal buffs, push lanes, counter jungle all day.

Other Good Summoner Spells
Ghost - Move fast and junk.
Flash - Hop over walls.
Heal - Mundo has stupid heal baits.
Cleanse - For healing debuffs.

Okay Summoner Spells
Ignite - OH MAI GAWD DAMAGES.
Surge - I AM BIG MUNDO LOLOL.

TROLOLOLOL Spells
Clarity - Get that Manamune Mundo.
Promote - Why did they put this in?
Teleport - Meh.
Clairvoyance - Even supports are not using this.

STARTING JUNGLE ROUTE

& OR &
If you want to counter jungle and gank then you should start with the cloth+5 option. But if you want to just gank early and not counter jungle, then you're going to go with the boots. Take your pick, but i like cloth+5.

BOOTS OPTIONS

OR OR
Heavy magic damage team? Get Mercury's Treads. Heavy AD team? Get Ninja Tabi. Don't care? Then Ionian Boots of Lucidity are for you.

CORE ITEMS

Heart of Gold
It's mainly just an early boost item. It gives you something for your ultimate to scale off of and your passive and gives you GP10 which will later be built into a great defensive item called Randuin's Omen.

Spirit Visage
This is the best item for Dr. Mundo. Cooldown reduction, health and increases your health regeneration. Which actually makes your level 3 ultimate heal you for basically another whole Dr. Mundo. It also increases your passive health regeneration.

OR Warmog's Armor or Frozen Mallet
Because a nice, large health pool on Mundo is key. The option between the two is up to your team comp or if you're going AD Mundo. Don't have much chasing power or you want to go AD? Get Frozen Mallet. Want to just have ******ed amounts of health and be super tanky? Then get Warmog's Armor.

OTHER ITEMS

More Magic Resist:
Wit's End - Recommended for any tanky DPS champ.
Force of Nature - For ridiculous amounts of health regeneration.
Aegis of the Legion - Cheap tank stats for you and your team
Maw of Malmortius - Combined with Blunt Force Trauma can give you ******ed amounts of extra attack damage.
Quicksilver Sash - Healing debuffs are annoying.
Guardian Angel - HAHAHAHAHAHA. MUNDO NEVER DIE.

More Armor:
Sunfire Aegis - Stack AoE magic damage DPS.
Atma's Impaler - For big auto attack damages.

TROLOLOL:
Rylai's Crystal Scepter - More health, and makes Infected Bonesaw and Heart Zapper slow.
Trinity Force - TONS OF DAMAGE.

You have quite a lot of options to start your route with Dr. Mundo. My personal favorite is starting at your wolves and blue. The key to it is making sure you ask for a strong no-smite leash. After killing blue buff, take a point in Infected Bonesaw and run to their red. Take it. You can typically finish it and gank top lane before their jungler finishes their wraiths. If you want, you can wait inside the red bush for their jungler and kill him as he walks by or just go gank a lane. After stealing red be sure to go get your red, otherwise your counter jungling was useless and you and their jungler are even.

Ganking is pretty self-explanatory. HIT THE DAMN CLEAVER. However, if you're going for first blood you can just lead with Exhaust and they will go nowhere once you hit them a red buff auto attack and an Infected Bonesaw. Remember that your main source of early damage is Heart Zapper and to have it up as long as possible during the gank. Be sure to chug a health potion before ganking because of this reason, Heart Zapper drains health like a mofo.

In conclusion, i hope this has been somewhat enlightening to you all about the big fat Dr. Mundo jangle. He is a really fast jungler and extremely strong tank. With enough health and the right items backing him, he doesn't care about ignites or healing debuffs. He is strong. He is too strong for you.