Unkillable mundo that can go where he pleases.

Run into entire enemy team, with back up if you're a wimp, hit w, then activate e and q whenever they are off CD. Preferably, use q on and basic attack dmg ppl who have little health. Use ult when you are down to about 20-30% health. If they are heavily fed and you have to retreat don't worry: YOU ARE MUNDO AND MUNDO GOES WHERE HE PLEASES.

Take cleanse to get rid of ignite and grievous wounds which completely destroys your healing. Offensively, you can take exhaust. It will make you take less damage from the target thus making you the really unkillable mundo (This especially helps against vayne's bolts as far as attack speed). Ghost is a powerful defensive spell that is my personal favorite because I can replace boots with ghost allowing me to get another item, though flash is also available if you really want it. Personally, i prefer ghost when playing a tank (especially if im not taking boots) but its up to you.

Pretty much max tankiness. Instead of the points in the offensive tree you can also have a tree fully invested in defensive for if they have a lot of cc.

Pros:
Incredibly tanky and his ult has massive health regen.
Deals high damage for a tank.
Good poke that helps counter other tanks.

Cons:
What cons? He's mundo. (Though igniting when he ults and percent health damage may actually make a slight nick in him)

Massive health to increase his health regen from his passive, warmogs, and ult. Atma's gives you 108.5 AD in addition to some bonus armor (With 5 WarMs). I don't think mundo actually needs boots as long as you know when to abandon a fight. Ghost/flash/exhaust/ult should be able to get you away as long as you don't stay too long. If the enemy team is heavily Ad, build randuin's. If heavily AP, or you just like extra regen and healing, build Spirit Visage.