“ 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”
“ Mazetown stands right around the entrance to the Maze, and its whole economy depends on the people coming to visit the ever-changing and apparently sentient dungeon. They don't get all that many visitors, but the ones that do come tend to be rather generous in their spending; after all, if anything you take inside vanishes as soon as you go in, and everyone who manages to come out usually does so with fabulous treasures in tow, why not spend your coin on R&R before getting started?”
“ A powerful wizard that the PCs encounter is completely silent. He does not speak and cannot be heard as he moves. Even his spells are silent, but his magic is just as potent.
He has a tendency to summon invisible chairs, place foes in invisible boxes of force, and other 'mime tricks'.”