“ 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”
“ Near a major city, a mirror image of the place has appeared. This strange double is infested with hostile insectoid humanoids that appear to match the city folk in numbers and armaments. The humans' diviners have determined that the secret of the city's appearance can be found within the double's college of magic, so heroes are needed to explore within this mirror city and discover what has drawn it from its distant realm. There isn't much time to spare, as the bug folk find their mammalian counterparts unnatural and blasphemous, and plan to destroy them.”
