One of the old, but more recent, edits I did involved using a mutator with monsters called WarNukingGround. All the monsters' attacks are some form of redeemer or nuclear explosion, and if you can take some of their weapons... they have guided missiles that can turn around corners:
So, I have this demented idea.
We need to get somebody to create a new kind of redeemer with legs, quadroped like a dog. When fired it will pursue it's target anywhere, not very fast but fast enough, and if someone runs through a door that closes, it will wait outside until the person is somewhere it can get to.
Partially inspired by the Smart Rockets mutator which makes the rocket launcher fire rockets, without legs, that will fly a long time and can turn corners to get whoever they're locked on.