“ 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”
“ A small, enchanted chest, 2 feet on a side. It is of some dark wood with fantastical images graved upon it. Worn leather straps act as hinges and a simple toggle keeps it closed. Anything placed within it, with the lid closed, becomes accessible to anyone with one of the other 5 identical chests. Once it is taken out of any one of the 6, the chest is empty again. Perfect for passing messages or small items between widespread groups, such as ships at sea and their ports of call or generals on the field of battle.”
“ The characters are given the task of transporting a flask of highly volatile liquid a long distance. The flask cannot be shaken too much or it will explode. The adventure involves stormy sea-voyages, bumpy cart rides through densely populated towns and horseback combat. In short there are many opportunities for it to break and explode.”