Kill the first two adds. Steelbreaker should be the last council living, this is the easy part.
Now everytime a player dies Steelbreaker heals himself 50% (25% with debuff) and gets 25% more dmg. The Maintank get a debuff that kills him after 20-30 seconds (heal + more dmg!).
Now just tank Steelbreaker with a Voidwalker pet. The pet will get the debuff and die, but Steelbreaker won't heal himself thisway, what will make this hardmode really easy. ;-)
gl hf farming hardmodeloot ;-)