Hello this is Succ, I just recently hit play primarily playing Mundo/Jax jg and thought I would share my builds :)

Mundo has very good camp clear, but he is very weak while doing it. Once you get over the hump of his early game, if you don't get bursted down, he is very strong.

Pros

Chonkiest Mofo in the game
Does good dmg with Q and E
Can solo obj relatively easy
Built in MR with W
Once you get 3 items you have achieved MundoMode

Cons

Can get shut down early
If bursted his health regen is ineffective
Weak first clear

P-Adrenaline Rush
Dr. Mundo passively regenerates 1.5% of his maximum health every 5 seconds.
Q-Infected Cleaver
COST: 50 / 60 / 70 / 80 / 90 HEALTH
COOLDOWN: 4
ACTIVE: Dr. Mundo hurls a cleaver in the target direction, dealing Magic damage magic damage to the first enemy it hits and Slow icon slowing them by 40% for 2 seconds.
MAGIC DAMAGE:
20 / 22.5 / 25 / 27.5 / 30% of target's current health
Infected Cleaver has a minimum damage threshold, and is capped against minions and monsters.
MINIMUM DAMAGE:»
80 / 130 / 180 / 230 / 280
If Infected Cleaver hits an enemy, Dr. Mundo heals for 40% of the health cost, increased to 80% if it kills an enemy.
HEALTH REFUND ON HIT:»
20 / 24 / 28 / 32 / 36
W-Burning Agony
COST: 10 / 15 / 20 / 25 / 30 HEALTH PER SECOND
COOLDOWN: 4
MAGIC DAMAGE:
10 / 13.75 / 17.5 / 21.25 / 25 (+ 5% AP)
TOGGLE: Dr. Mundo sets himself on fire, gaining 30% Tenacity and dealing magic damage every 0.25 seconds to nearby enemies.
Burning Agony can be toggled off after 0.5 seconds of toggling on.
If Dr. Mundo's health falls below Burning Agony's health cost while toggled on, the ability is toggled off automatically and put on a 1 second cooldown.
E-Masochism
COST: 25 / 35 / 45 / 55 / 65 HEALTH
COOLDOWN: 6 / 5.5 / 5 / 4.5 / 4
Masochism
PASSIVE: Taking magic damage or paying a health cost increases Dr. Mundo's Magic resistance by 3% for 2 seconds, stacking up to an amount.
MAXIMUM MAGIC RESISTANCE:»
6 / 15 / 24 / 33 / 39%
ACTIVE: Dr. Mundo gains bonus attack damage for 5 seconds, increased by an amount based on his percentage missing health.
FLAT BONUS AD:
40 / 55 / 70 / 85 / 100
MAXIMUM MISSING HEALTH BONUS AD:»
20 / 35 / 50 / 65 / 80
Additionally, Dr. Mundo's next basic attack within the duration will cost health, but gains 25 bonus range and deals Attack damage bonus physical damage.
BONUS PHYSICAL DAMAGE:
3 / 3.5 / 4 / 4.5 / 5% of his maximum health
Masochism resets Dr. Mundo's basic attack timer.
R-Sadism
COST: 25% OF CURRENT HEALTH
COOLDOWN: 110 / 100 / 90
ACTIVE: Dr. Mundo regenerates health over 12 seconds and gains bonus movement speed for the duration.
TOTAL REGENERATION:»
50 / 75 / 100% maximum health
BONUS MOVEMENT SPEED:
15 / 25 / 35%

Raps-Red-Krugs-reset and buy Ruby Crystal-Wolves-Blue & Gromp Simultaneously- Scuttle

Start W, stand in the middle of them and hit the Large Rap. As the small Raps die kite towards Red Buff. Use your first pot. Take E second, kite the buff towards Krugs. Be sure to use your E as an auto reset. After Red use your second pot. Finally smite the big krug and clear them normally. After you reset kite wolves towards Blue, saving a Q to throw thru the wall to bring it to you. While taking Blue, take gromp as well. You will need to smite, but will finish the camps anywhere from 3:15-3:20. This will give you a lvl 4 advantage at Scuttle.

This is my first guide so I hope its helpful, thank you for reading this far! :) Be sure to comment if you have any questions/suggestions and please like the guide! My op.gg if you are curious https://na.op.gg/summoner/userName=i%20succ%20boys69