Really useful passive, that allow Mundo be a nice tank. More better, that Garen Passive, because Garen regen out-combat. Mundo healed always. With Mundo Ult, Spirit Visage, Force of nature, Warmog, we will recieve very big HP regen.
You shouldn't underestimate it. Include Spirit Visage, and it will become higher. It also fits Mundo extremely well, since his major thing is hp-regen.
About building Mundo as a tank, he is extremely nice as OT (or even MT) and you don't build him as a tank because of the passive, but because of his ability to hurt a lot even without having a lot of gear that increases AD.
Mediocre passive
Often causes people to build Mundo like a tank however when he doesn't fit that role very well
This is per second though so its 1.5% per 5 seconds
1000 hp - 15 hp/5sec or 3 hp/sec
2000 hp - 30 hp/5sec or 6 hp/sec
3000 hp - 45 hp/5sec or 9 hp/sec
About building Mundo as a tank, he is extremely nice as OT (or even MT) and you don't build him as a tank because of the passive, but because of his ability to hurt a lot even without having a lot of gear that increases AD.
Often causes people to build Mundo like a tank however when he doesn't fit that role very well
This is per second though so its 1.5% per 5 seconds
1000 hp - 15 hp/5sec or 3 hp/sec
2000 hp - 30 hp/5sec or 6 hp/sec
3000 hp - 45 hp/5sec or 9 hp/sec