1) He came back from the dead
But God raised him from the dead, freeing him from the agony of death, because it was impossible for death to keep its hold on him
2) He encourages zombie like behavior
Jesus said to them, "I tell you the truth, unless you eat the flesh of the Son of Man and drink his blood, you have no life in you"
Excerpts from The Uncyclopedia's article on Zombie Jesus.... - OMGeek
It was as the subtle, burning glances of His onlooking Roman captors, the angry, Jewish rabble, and remorsefully sullen followers became more stricken with terror, fright, and penance that Zombie Jesus returned to this world, forcing his broken, tired limbs, blood-stained from the mortal wounds he had suffered, to pull his undead carcass from the rough hued Cross so that he might seek the most appropriate Earthly sustenance deserved of the sacrificed son of God: a crimson river of Flesh and Brains to satiate his heavenly hunger.
After dying, Jesus was raised from the dead and once more walked among the living. This, of course, would only be possible if he were a zombie; Zombie Jesus is the identity of Jesus following the Resurrection. In zombie form, Jesus retained his unending love for mankind, in particular, he loved their sweet, delectable brains. Many of his followers were surprised when, instead of offering God's salvation, Zombie Jesus voraciously consumed their faces.
It is now widely believed today that Jesus was the source breeder of modern-day zombies, since when he resurrected, he infected his disciples with the blood of the new "Holy Alliance", thus founding the basis for whole new era of zombie mayhem, unseen since the infection of elite Greek philosophers by Zombie Plato several centuries before.Teachings and Acts of Zombie Jesus
Zombie Jesus' words and acts are recorded in one of the apocryphal books (books which were not included in the New Testament by the Catholic Church), the "Book of Brains". The most famous part of the "Book of Brains" is the "Parable of the Brains", in which Zombie Jesus spoke unto the assembled masses: "Braaaiiins.... braaaiiinnnss... braaaaiinss!!" (in the original Greek of the Gospel, "μυαλό.... μυααααλό.... μυααααλό!!!").
Defeating Zombie Jesus
Unlike the common zombie or the common Jesus, Zombie Jesus is notoriously difficult to put down. The garden-variety zombie can be killed by a shovel to the brain, but only the Soviets (and Cthulhu armed with a pair of Sephiroth-chucks) could defeat Zombie Jesus... He was mutated back into the form of a man, which was very short lived for he was quickly killed by a Nazi, because despite being a former Messiah, zombie, and Kraken, he was still a Jew, and Nazis hate Jews..
The debate over whether Jesus came back as a zombie or a vampire caused yet another schism in the Christian Church, and forming two new Christian denominations: Zombie Christians and Vampire Christians. About half of the population of Vampire Christians claim that they converted because "Vampires are just so much more awesome than zombies". These people were insane, of course. Zombies are far superior.
A link to the Zombie Jesus web site
A link to the Uncyclopedia's article on Zombie Jesus