Okay don't take this personally but I do not play jungle so I have no intention of making a guide for junglers. I would have to make an entirely new guide for jungle and I do not play jungle at all. I don't want to give the wrong information and I do not have the drive to make a new guide for jungle, that is literally it. You might find some of the info useful for junglers as well, but I am not going to make a guide for jungle unless I am going to start playing jungle a lot.

I think NattyNat plays a lot of Mundo jungle, he usually goes Heartsteel rush and then something like spirit visage or dead man's plate or titanic hydra. I don't really play mundo jungle either so I'm not entirely sure what to build myself.

I actually do keep it updated, I just don't really like the Warmog's style rush, and this is how I personally think matchups go for Mundo. For example I know Alois says Nasus is a free Mundo matchup but I personally find it really tough to play into if the Nasus builds correctly, he just straight up runs me down on side lane.

You can run Spellbook instead if you want to into those ranged matchups, I just personally like Grasp more. I like to go Bramble into a lot of matchups because I like to play more teamfight focused/mid game 1v1 power spike Mundo. Jax can go Blade of the Ruined King and if I have Warmog's + Heartsteel I can never walk up to fight him, literally ever. He legit needs to be like 20% health and I have to instakill him when I fight him or else he unironically beats me because he heals off me due to Blade, and this is the case for a lot of matchups. You can go Warmog's + Heartsteel into Sett, but if he has Blade and hits you with auto+auto+2 q autos you lose half your health instantly (I tested this). He can even dive you from close to full health with his full combo without even needing his w to be stacked. I hate just doing the hit and run playstyle for Mundo unless it's the only way to realistically play out the lane. I like Heartsteel because of the damage it provides and the duel power. Heartsteel + Bramble + Visage + Plated into Jax allows you to sit in melee range and beat him from full health every single time. Sure, you don't hyper sustain after fights, but you can actually walk up and beat him down in the melee 1v1 and not have to rely and the Warmog's heal cheese, and then if you actually get ganked on, like 2v1/3v1, you don't instantly need to run away, you're tanky enough on both armor and magic resist to sit there and fight it out, because with the other setup all you can do is go back and heal cheese to full health after every trade. It also means that % health physical and magic damage won't completely murder your health because you don't have any bonus armor or mr. Take Warwick Q that deals % health magic damage. Imagine you have no bonus mr and his q is fully maxed and he has Blade of the Ruined King. He will unironically heal 500 health INSTANTLY from you because you have so much health, or he can instantly ult you and go from 100 health to 2000, I'm not kidding, and this is the case for A LOT of matchups. Some examples are: Sett, Jax, Mordekaiser, Irelia, Varus, etc. This is also why I like Plated more, it reduces even more damage from stuff like Jax auto attacks, Sett auto attacks and Q, Garen Q, etc. I like to actually play up and force fights rather than perma cheese heal after a trade, it's just a personal playstyle thing.