why is mundo doing so much damage to me even tho he had 5k hp

... Mundo scales off of hp and does magic damage sooooooooooooooo...

Did you build MR?

Dr. Mundo hurls his cleaver, dealing magic damage equal to 15/17.5/20/22.5/25% of the target's current Health (80/130/180/230/280 damage minimum) and slowing them by 40% for 2 seconds. (Max 300/350/400/450/500 damage to Monsters)Half of the Health cost is refunded if the cleaver hits a target (increased to the full Health cost on killing blows).

The more health he has, the more damage his E does as well

So why haven't they nerfed his damage? a 5k fucking tank deleting squishies?

According to Riot, Mundo is actually a fighter, not a tank. So they're going to want him to do damage. But I think we all know the guy is one of the heaviest tanks in the game. Personally, I think he would be fully balanced if they made that first hit on E do reduced damage to champions. I'm sure they buffed it to help him in the jungle since his jungle in season 5 was completely behind any other jungler even though he was designed to be a jungler. But now it gives him a crapload of early game power when he's supposed to be a late game champion.

You had zero MR

Well, he's supposed to do 25% of your current hp with those. If you don't have any MR and especially if mundo specced into some magic penetration in his runes it's going to hit for a lot. Either don't get hit or get some MR.

Let me use the juggernaut excuse. He has no mobility outside of movement speed buff and no hard cc. Also buying an item shuts down 40% of his biggest strenght