So I've been on a winning streak lately with Mundo and after telling the opposing yi to buy mandreds I saw him highlander my health to nothing in a few quick seconds. Bad idea I know. For the rest of the match whenever I was in a teamfight situation I would almost immediately pop up my ult and tell my team to focus fire yi first when he alpha striked us. Is that the only thing I can do about a champion fighting with mandreds? Run away like a ***** and ask my teamates to focus him? Does magic resist do anything and is it even worth it?

tl;dr Is there an effective way to counter mandreds if you are Cho or Mundo or any health stacking off tank?

Well I'm playing Mundo and have to tank because no one else wants to so I kind of have to stack health since it helps with the abilities. How much does magic resist take off from mandreds anyways?