- Go to the nether.
- Spawn a zombie villager.
- Cure the zombie villager (weakness potion + golden apple).
The zombie villager gets red particles, and after waiting a few minutes it converts to a villager.
The zombie villager gets red particles, and after waiting a few minutes the game crashes. Whenever you try to open that world again, the game crashes. So, the world is permanently broken.
I have a villager converter in the nether where I zombify a villager, shoot it with a weakness tipped arrow and then I heal it with a golden apple. After a few minutes of the zombie shaking it the game crashes and whenever I try to load back into the world it crashes. The world is purely survival, the zombie villager was in a minecart when I tried to cure it, and the zombie villager was a librarian.