Red dragon is immune to lone heroes, so as long as his ability is active, human heroes can do nothing to him. If the human has greater toughness that Red Dragon's strength, the battle is in a stalemate, otherwise Red Dragon is beating the human hero. If the dragon's ability is negated (by enhancement special ability, hero special ability, artifact, etc.), then the heroes can then affect him. Also an ability that functions regardless of immunity (plague of frogs) gets affects red dragon anyway. And if all else fails, you can get rid of red dragon with a card not used by the hero (say a dominant like Angel of the Lord, is discard him when you are blocking with forest fire, etc.)
