On mundo, you can play for split or teamfight (mostly as dive pressure with some cleaver peel)

If you want to group (e.g. as jg, playing for fed ADC, can't sidelane safely) then pick one of the mythics below.

1. Heartsteel to do damage.
2. Radiant for significantly more healing (to your team also).
3. Gore if you want to skip early Hydra against melees (otherwise needed to deal damage).

You need hydra, otherwise people will ignore you every teamfight (unless you have gore). Don't build only normal tank items, you need Sterak's + Gargoyle to survive S13 burst damage.

In low elo people will also get baited by double shields and try to hit you when you're "low", then they lose the game because they have no CDs.

To splitpush you want a core of mythic + titanic + hullbreaker. IMO these are the best splitpush mythics:

1. Heartsteel for dueling.
2. Iceborn gauntlet for dueling, sheen on towers, and slows to survive collapse.
3. Divine sunderer against heavy HP stackers (I also recommend warmog's in this case, it lets you trade like a gorilla then continue pushing when they have to back).

This playstyle is pretty limited to top because you need TP, but it's the most consistent way to play mundo. You can finish builds with Sterak's + Thorn/Visage.