“ 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”
“ Dust Elemental
https://gatherer.wizards.com/Pages/Card/Details.aspx?multiverseid=1594
At the corner of air and earth elemental planes resides the dust Elemental, a growing threat to Parisia. With it's powerful choking attack, this creature is a threat to the city. More and more of them are appearing in town, spawned from the many dust devils, a frequent foe of the party, they come in size from 3 HD to 20 HD. Why are there so many? Why in the city?”
“ Trying to find a place for this...
'After the famine hit the land, the priest Galen began religious wanderings, drawing his congregation to follow him. Those who took up with him, began to walk, a great outpouring of energy to this religious pilgrimage, coming from an impoverished nation with no true direction other than to find relief. Galen professed to his followers that they would find great resources set by his God down on Earth for them, enough to nourish and slate their thirst. Those that fell as he took them across the barren plains of the western reaches, rose again to join the lines. When finally all had died, Galen led them further, praising Nuh-Erell for that first city they came upon and a feast of flesh that lay in wait'”
