Minecraft wiki entry for Totem_of_Undying, associated text: If the player is holding a totem of undying in their off-hand or main-hand slot and receives otherwise fatal damage, the totem saves the player from death. The totem of undying must be in the player's hand (main hand or offhand) for it to work—it does not work if it is in the hotbar, unless selected. Any mob that can hold a totem of undying (in a hand or in the mouth) can use it while holding it. The totem can be used only once; it disappears after use. It does not save the player from death caused by void damage or the /kill commands.