Playing The Walking Dead by Telltale Games has gotten me in the mood for zombie RPing. But since personal things tend to pop up in my life when I least expect them, I don't think I could GM this all on my own. If you like this idea, you've got all the permission I can provide to use this for one of your own RPs.
What got me thinking of this is that I've used a 3 stage infection system in past RPs, to combat the obstacle of scientific realism in the form of body decomposition. With realistic decomposition in mind, a zombie outbreak would be over within months if the zombies ate without any practical benefit to their consumption. Now to make things a little more interesting, I've thought up a 5-stage infection system for zombies.
Stage 1 would be where the victim would still be alive, conscious, and still be capable of talking, tool/weapon usage, and other regular functions, but would have been rendered insane and extremely violent. Take a look at the titular infected of the Crossed comics for reference. This stage would last for a day after infection.
Stage 2, the victim is still alive, but has deteriorated to feral instincts, and can no longer display sentient functions. Think of the common Infected from the Left 4 Dead series. This stage would last for about a week.
Stage 3, the victim is pretty much undead at this point, much like the zombies depicted by George Romero, Max Brooks, and The Walking Dead. But here's the scoop. Rather than eating for no goddamn reason at all, their decomposing bodies need to eat in order to make it to the next stage of infection. If they go a month without feeding, their bodies would have rotted away to the point of no longer being functional.
Stage 4 is when mutations start taking place in the undead. This is what Stage 3 zeds need to consume flesh for, so that they could combat their rotting and continue killing and spreading the infection. The mutations can range anywhere from sharp claws to overextended muscles bulging through the skin, and anything else you can think up. Think of the special Infected from the Left 4 Dead series.
Stage 5 is when Stage 4 mutant zombies have eaten enough flesh to reach this stage, where the brain is no longer vital to the zombie's survival, and the Stage 5 infected can take in multiple bodies to add to its mutated form. Think of the Necromorphs from Dead Space.
Let me know what you think.