Minecraft wiki entry for Advancement_guide, associated text: Before attempting this advancement, you must go to a woodland mansion or initiate a raid, and kill an evoker, which will drop a totem of undying. Then, if you take fatal damage while holding the totem of undying in either hand (switch between hands by pressing F, better for dual wielding), you will not actually die; instead, your health will regenerate (from Absorption and you gaining 1) and you will get the advancement.