I have a basic concept for the game down, but I'm still iffy of alot of the details. Please feel free to critique or advize as you feel fit.
I don't know what lvl to start at (thinking 6), but I know for a fact that its gonna be hard for them. I want several chambers culmulating in a boss fight, and I expect several players to die along the way.
Now, the fun part. I want the deceased characters to still be usefull. So when they die, I want them to become ghosts. I was thinking that every room could have traps or triggers only effectable by the ghosts.
For example, 1 room could be layed out like a tic'tac'toe grid, with the ghosts able to raise and lower wall sections within the room. All the while, another ghost is able to trigger penatrating line arrow traps allong the outter walls.
1 room could have a statue the ghosts can possess while the others knock lanterns off the walls onto foes.
Finally, I'm not quite sure what the boss will be, but for the last room, the ghosts can try to tie the BBEG down or something like that, while the living chip away at him. The more ghosts, the weaker he is, but the more living, the more damage done against him. As long as 1 player survives, the game continues.
They could also "ghost grapple" the lower opponents to hinder them in some way.