“ 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”
“ The PCs have travelled long and far. As nightfall approaches a mighty storm is unleashed. Luckily there is a lush wood nearby the path.
A good shelter for the rage of the unnamed weather gods it seams at first. As the PCs enter under the roof of this dense wood, they are welcomed by only a few drops wich is allowed trough the thick forest crown. A fire is offcourse required to warm the weary bones of the travellers. As one of the party is set to the task of collecting firewood the others settle down at a suitable location. But alas, they did not know the perils of this forest. But it seems clear to the rest of the party that something ill is at work as the woodcutters scream echo from afar.”
“ Most large mammals, such as elephants, rhinos, and their modern ilk are ill-suited for domestication, but that doesnt exclude their use as engines of war. Rather than raise and train the Mammoth from birth, Mammoth Handlers instead capture the wild Mammoths at a young to juvenile age and train them for war. These animals are draped in armor and are unleashed as living war machines against the foes of the Mammoth Tribe.”