Mundo Needs Help
Mundo's not really viable anymore as either a jungler or a top. He hasn't been good top in a long time because he has relatively poor teamfight scaling while also not being a dominant laner. A Maokai is just about as tanky but provides so much more to the team. Sion is another example but has a great engage. Mundo's not doing enough more damage to really justify the pick over countless other tops. This meta is also more mobile than ever and so it's hard to function vs good players without a gap closer. I love Mundo's spammable Q and don't mind his kit but he needs more raw power to have it work.
As a jungler, Mundo was a decent pick last season because he could clear fast and get tanky enough to secure map control/objectives early on. Now, it feels like Kha, Jax, Lee etc. all have an easier time destroying him early. His clears are far less safe. It's harder for Mundo to get the gold lead he needs to be tanky enough to have influence. He no longer powerspikes mid game to the degree he needs to merit picking. He was never great early or late (at least vs competent teams) but last season I was nearly unkillable after Ninja Cinder Warmog's and SV. I had until 35-40 minutes to be very strong and generally got gold leads from counterjungling/farming faster. Maybe it's the Cinderhulk nerf and the new runes too but he feels so much weaker even late game.
My suggestion: +4 base armor early - his clear is less safe than ever before ^^^a big part of what made him viable last season was taking scaling armor + Armor Quints and being relatively tanky early on too
I'm guessing that this isn't quite enough (especially if Ninja Tabi's get nerfed and Cut Down gets buffed) but it's a start and probably brings him to the edge of viability. I was going to suggest buffing his base MS but honestly, I think that 5 more MS along with the clear buff of 4 base armor might make him too strong. I'd have suggested 2 MS but I just don't see you guys work with numbers like 347.
Would all instantly become pretty viable on him.