Passing of the Age

Complete Mister Mushroom's questline - he's the "Herald". The wandering Mister Mushroom pops up at a set of specific spots across Hallownest (Fungal Wastes, Howling Cliffs, Kingdom's Edge, Queen's Gardens, Deepnest, the Ancient Basin and more); visit and speak with him at each in the right order. It's part of the Godmaster update and the final steps open up once you've reached a main ending. Talk to him at the last location and he passes on - you get a "To Be Continued" screen and this achievement. Follow a location/order checklist, as it's easy to do out of sequence.