“ Perhaps the product of another universe or time, this vessel appears as an early Tall ship, but is made of iron from keel to spar. The sails are a battered canvas but are nearly indestructible, but in truth do little to move the ship - the ship is able to move even with no winds.
The ship is powered by life force, requiring regular sacrifices to ‘charge'. The victims are cast in front of the vessel as it moves, it's razor sharp bow bisecting them. The ship may initially be missing key components and the ritual to power it would also require research by would-be users.
The ship has no built in weapons aside from the bow, which can easily cut even large wooden ships in twain.”
“ 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 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'.”