size mutation

I have no idea if it's easily possible:
The survivors don't slow down as they loose health and they never end up lying. instead, There's a mutation that makes them shrink in size depending on how much health they have, so from their own point of view, they're running about just as fast but when they shrink, it's obviously going to take longer to get from one place to another. it will also make it more difficult to jump up on things, so they'll have to go round stuff instead (like when you're crawling) but they'll still be able to climb ladders.
They'll have the advantage of being harder to spot by the infected when they're weak but the dissadvantage that they'll be harder to spot by the survivors too, when they get snagged by the infected.

could be interesting.

 

That would be quite hard to do with the kind of scripting we can do. You should ask honorcode23 about it. He does all the server plugin scripting.