The passenger said, “It sounds like your wind chime is broken, or at least out of tune.” The first mate just smiled. “That chime is music to a sailor’s ears, it is,” he said. “We will have smooth sailing this day.”
Rather than making a baddy impossible to hit, consider giving it mega-hit points.
Super hard to hit leads to great player frustration. Allowing them to do damage leads to a sense of accomplishment. another variation of this would be to give the bad guy a forcefield that shows damage.You could also give them a mastermind ability that sluffs the damage of to minions who should be easy to kill.Once in a while a super high to hit encounter is ok ,but it should be few and far between.
Your mileage may vary