I like the idea of leading under a trap door. That would be an easier way of killing the thing. (But truthfully if you look at the graphics of the trap doors, there is ground under them. A single trap door in the center of a pit appears as a pillar.)
Well, the only other thing that I thought of was a steel golem.
This monster acts like a roach only, its indistructable in its original form. A new item, The Magnet, would be added to Golem levels and the golems would be attracted to them. They would pursue you until they walked in front of a magnet, then one turn at a time, be dragged in the direction of the magnet. When they hit the magnet, or any other solid object in its path, the magnetic force would tear them apart.
Also, if beethro walked past a magnet, he would spin so that his sword was facing it. This could easily mess up an attack by forcing your back to on coming monsters, or help turn you arund to deal with that otherwise impossible to kill roach that snuck up on you.
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There are but two paths through life, and a wise man walks them both.
Eccept the things you cannot change, but change the things you can't eccept.