Mundo's healing: (75% HP x 1.3) x 0.6 = 58.5% HP over 12 seconds or 4.875% per second.
Mundo would have ~2700 HP at level 15 with Resolve runes and his items. That means he heals 131 HP per second from ult.
Now passive: (0.3% of HP per second x 1.3) x 0.6 = 6 HP per sec.
Now HP5: (18 + 18 + 18) x 1.3 = 70 or 7 hp per second x 0.6 = 4.2 HP per sec.
Let's assume he has Second Wind. Calculating this is a bit hard, but we can assume he averages around half his HP.
6 + 4% of 1350 x 1.3 = 78 hp per 10s or 7.8 hp per second x 0.6 = 4.68 HP per sec.
Now his MR: 48.7 + 55 + 55 = 158.7 MR. We can also assume that he got hit a few times or used a few spells, so lets give him 10% extra MR from his E. A total of 174.6 MR.
Let's look at your MR pen. Just 33. Which brings his MR to 141.6.
141.6 MR reduces about 59% Magic damage.
So, Mundo restores 146 HP per sec and reduces 59% magic damage.
Say you have 300 AP, 260 from items and 40 from runes. We'll also assume that your
is fully stacked.
Your Ult will deal 275 + 240 damage = 515 damage and 10% + 3.75% over 2.5 seconds or 375.25 damage.
deals 2% per sec since he is CC'd. So that's 5% HP damage or 135 damage.
So with
's damage boost:
Ult Beam: 566.5
Ult Pool: 412.8
Torment: 148.5
Now, Adaptive Helm.
Since Ult ticks every 0.25 sec, total of 10 ticks, so 9 tick deal 80% damage = 82% damage or 464.5 damage.
Since Pool tick every 0.5 sec, total of 5 ticks, so 4 ticks deal 80% damage = 84% damage or 346 damage.
Since Torment ticks every 0.5 sec, total of 5 ticks, so 84% damage or 124.7 damage.
Total of damage post MR: 383.4 damage...
He heals for 365 over 2.5 seconds...
So Mundo just takes around 12 damage...
This goes to show a Healing anti-mage tank can out heal a mage without a Void Staff. Build Void Staff kids. If you had just Void Staff's passive, you would've dealt 41% more damage to him.