I planned, but sadly never played, a zombie survival game and did some serious thinking about the slow zombies versus fast zombies decision. I happen to think fast zombies create a nice sense of terror, but slow zombies surrounding a building and preventing the PCs from escaping is a lot of fun and can lead to some very good roleplaying. I came up with a few basic examples of zombie types, use them if you'd like.
Sprinter: A zombie of a freshly killed person, the body is still as close to normal as it can be. Muscles function in all the same ways and the brain has had little deterioration. Sprinters are focused killing machines that move in instinctual packs and attack based on smell and sound. A sprinter can climb, run, and even swim in a spasmodic fashion. The body is still dead however, so a Sprinter is not quite as fast as it was in life.
Walker: Three hours after death the effects of rigor mortis set in and Sprinters become Walkers. A Walker moves at a slow, painful looking lope of about a normal persons walking pace. Walkers look more or less alive, skin tone may be pale or large bruises may appear where blood has settled in lower extremities. During this early stage, before full rigor sets in, Walkers wander the streets and react to fast movements or loud noises. After about twelve hours of death rigor mortis sets in fully and the muscles seize. At this point a Walker becomes a Crawler.
Crawler: A Crawler is either a zombie with crippled legs (destroyed or removed) or is a Walker in the 48 hour period of rigor mortis. A Crawler uses hands, even finger tips, to drag itself along, usually feeding on the helpless remains of victims before they turn or just die. A crawler may have a self preservation instinct that keeps it out of the open; they tend to skulk under cars or furniture waiting for a living victim to pass. If a Crawler gets ahold of a leg they latch on like bull dogs and tear at the calf muscles with their teeth. After rigor has passed, about three days after death, a Crawler’s muscles loosen and it can stand, once again becoming a Walker.
Shambler: After about four weeks of exposure to air and water a zombie will begin to rot, in rare cases even to liquefy. (see Rotter below) Most Shamblers are rotted bodies, missing eyes or large portions of stomach, but the bodies are still intact. A rotten zombie that loses its legs becomes a Crawler.
Rotter: A Rotter is an older zombie that has decayed but hasn’t burst yet, its body is bloated with gas and fluid. When a Rotter is killed it explodes in a shower of ichor and rotten flesh. A Rotter that has built up bile and waste matter in it’s stomach, identifiable by the extremely distended belly is a Puker. When a Puker is attacked in melee combat it violently expels this matter in a five foot stream potentially blinding and certainly incapacitating anyone in the path.
Hulking Zombie: A Hulking Zombie, or Hulker, is a zombie at any stage that had been especially large or strong in life. Football players, firemen, or body builders would become Hulking Zombies in death