How do I become a zombie?

Solution 1:

The Cursed Amulets of Resurrection have been changed to Cursed Amulets of Zombification. If you're wearing one when you're killed you'll become a zombie.

From the wiki description:

As of build 4.0.0, Amulet of Resurrection’s name was changed to Cursed Amulet of Resurrection. It became soulbound and you could buy it in Nexus for 1,000 fame, but there was a 5-10% chance that it would not work and you would be “zombified” (killing your character). It was rumored everytime a player died with an ammy, the chance to be zombified grew by 0.01, and that after 10,000 ammy breaks there would be a 100% zombification chance.

As of build 4.3.0, The Cursed Amulet’s chance to help you cheat death was evidently decreased, rough estimates suggest a resurrection chance of below 40%.

As of build 5.0.0, Cursed Amulets had a 100% zombification chance and dropped from the boss in the dungeon “Haunted Cemetery.”