Minecraft wiki entry for Block_and_item_duplication, associated text: This method is extremely deadly, but not necessarily to the player. This method involves taking a mob that can carry items (e.g. a zombie, a donkey or a llama) down to very low health (i.e. half a heart or less). Using extremely precise timing, kill that mob as it travels through an end portal or nether portal. The items equipped and the mob should appear in the other dimension. It works by tricking the game into thinking the mob is alive on one end of the portal and dead on the other side. The live mob will travel through the portal still carrying the items, and the dead mob's items are also sent into the portal, allowing the player at the other end to collect the cloned items and the mob carrying them.