1492mike

I will simply put it this way, new ideas for the special infected for Left 4 Dead 3 require a lot of creativity and careful thought. Here's something to think about (some of the posts have sounded pretty interesting though). The special infected of the first two games work with each other and have their own special abilities and attributes. In order for a special infected team to put a halt to the four survivors, strong teamwork should be in effect. After looking at some ideas other users have posted, I have noticed quite a few abnormalities in their abilities. Special infected that disable weapons and slow players tends to take away from the actual point of the infected's goal. Guns run out of ammo, and common infected are there to slow the survivors (which I often find upsets players enough as it is!) When survivors are already below 25% health, they move slower than molasses, with a special infected dedicated to slowing the survivors even more, they might as well be standing in place waiting to be killed. Once again, ideas for the special infected need to be new, creative, and functional with the other infected. It may be hard to come up with new ideas while maintaining originality and not having the special infected being too similar to other specials.  
An idea I've had swimming around in my head was a flying zombie (I haven't actually come up with a creative name for it yet) but I'm sure I'm not the only one who has thought of this special infected idea. An ability I had created for it would be to have it dive bomb the survivors, dealing a fair amount of damage, in addition to an effective hit, it actually pushes the survivor away from the remaining survivors, dragging him/her on the ground, then initiating its incapacitating attack. Think of it as a cross between a Hunter and a Charger, only difference is that it flies. 
  Another idea I've concocted was a burrowing zombie, hides in wait underground and pulls an unsuspecting survivor into the ground leaving half of the survivor's body exposed for the others to find him/her. I got the inspiration for this idea from the movie Eight Legged Freaks (in the movie, there are burrowing mutant spiders that grab humans and pull them under, killing them instantly). I already see the flaws with this infected idea, like how would you kill the zombie if it's underground? However it's work in progress.