“ 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”
“ A master thief is struck by an insanity spell and thinks he is half cat. He walks around sniffing things, clawing the furniture and licking himself in the manner of a grooming cat. This is a major cause of embarassment to the guild and the master thief must be cured of his insanity.”