|Season(s)||2, 4, 5, 7, 8, 11|
Zombies come in a variety of forms, raised from the dead by a Greek spell, by the demonic power of Samhain,and even raised by Death himself. Another group of beings that behave in a zombie-like manner are humans infected by the deminically engineered Croatoan virus, and those affected by the Leviathan food-additive.
When first raised, their memories and personalities may be intact, and they can behave like normal, rational beings for several days before becoming violent and cannibalistic. Methods of dispatch generally involve beheading, staking, or fire. Depending on the zombie, Sam and Dean appear to have varying success with each method. When Sam and Dean first encounter a zombie, a woman named Angela Mason, they seem overwhelmed by the amount of lore on the walking dead and how to kill them:
They shoot Angela in the chest and head with silver bullets, which seems to slow her down but has no lasting effect other than making her angry. Other lore Sam finds suggests "nailing the undead back into their gravebeds," so they lure her back to her grave, and Dean stakes Angela in her coffin, finally dispatching her.
When facing Samhain, he raised several zombies, one who attacked Samhain's vessels students, as such they encounter zombies a second time, Dean stakes two zombies in their coffins to dispatch them.
The next time they encounter zombies is in Sioux Falls, South Dakota, and Sam says that they can be killed with a headshot. Like ghouls, it seems that obliterating their heads can kill them. It is unusual as when Sam shot Angela in the head she recovered fairly quickly, though it may be due to the difference on how each zombie was raised.
People infected with the Croatoan virus, called "croats" by Future Dean Winchester, could be classed as zombies as they lose their sense of reason and become unthinking murderous creatures. They are part of the demonic plan for the Apocalypse.
Widespread distribution of the virus is planned using a new vaccine being produced by Niveus Pharmaceuticals, one contaminated with the Croataon virus. The vaccine is being rushed to stem an outbreak of flu caused by Pestilence. This potential disaster is prevented when Bobby Singer, Sam and Castiel blow up the distribution warehouse, although only after battling some zombies. Those infected with the Croatoan virus can also be killed by conventional firearms.
The next type of Zombie the brothers encountered, was created by accident as a side affect of the Leviathan plot to control and fatten up the population, 0.03% ended up increasing their metabolism. This allowed them to become super strong and agile but also made them cannibalistic and monstrous.
Through a series of horrible magical experiments on the native population, the Thule learned how to bring back the dead in 1942, however this version was more akin to resurrection, as rather than decaying, their reanimated members were still themselves, personality wise. However at the same time, it also caused them to cease aging, and the only way to kill them was shoot them in the head, and then burn the body.