Pushable walls will almost definitely not happen.
Magnetic walls have been presented before, although I called them
Iron Walls.
"
No-sword"
squares can be approximated right now with orbs that you cannot hit, and once JtRH comes out, with bombs.
The Roach-Snake thing needs more elaboration. It sounds to me like a "
Juggernaut"
...something that can never stop moving. You need to define whether or not it dies if it stops moving, if it's only one square in size, and if it is one square in size, if it can move backwards at all. Because if it can move backwards, then it's really not much different than a roach at all...it's just a roach that will move back and forth between two squares when it can't get to Beethro.
Game on,
____________________________
"
He who is certain he knows the ending of things when he is only beginning them is either extremely wise or extremely foolish; no matter which is true, he is certainly an
unhappy man, for he has put a knife in the heart of wonder."
-- Tad Williams