“ 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.”
“ Five main ingredients were used to create this noxious, real-world (ridiculously named), chemical compound, featuring sulfur as the main ingredient. The odor was said to be akin to rotting refuse, decomposing carcasses, and fecal matter. 'Who-Me?' Was developed during WW II by the OSS to aid the French Resistance against the Germans. The idea being to utterly humiliate and ultimately demoralize the enemy by making them stink of garbage left to rot under a hot sun.
The bizarre experiment did not last long however as 'Who-Me?' could not be administered on select targets (controlled), without making everyone in a certain radius, friend, foe, and sprayer alike, stink as well”