Passing of the Age is a Wish available late in Hollow Knight: Silksong, one featuring a character that may be familiar to fans of the first game. This guide will go over each step of the Wish, along with what you get for completion.
*Spoiler Warning: Do not read this guide unless you've already completed the final boss after doing the "true" ending requirements.
Passing of the Age

Silksong's version of Passing of the Age starts in the Putrified Ducts, all the way to the east past Fleatopia. In the top right corner of the cave, you can use Silk Soar to reach a hidden alcove. Inside, you find a tablet, triggering the wish.
As with Hollow Knight, you have to follow the hints given by the tablet to find Mister Mushroom, going to specific places in a set order. In most of the areas, you'll also have to use Needolin to make him come out of the ground. You'll know you're in the right place to do this if there are a bunch of blue mushrooms in the ground. After you talk to Mister Mushroom once he pops up, he'll then leave for the next location.
"Under Chapel fallen to the monarch's might,"

After dropping down into the ruined chapel in Moss Grotto, head right.
"Over camp collapsed to the black thread plight,"

From the first location, head back up and into Bone Bottom. Mister Mushroom is on a platform to the right.
"Scorched field on edge, shells black and burned,"

Head almost all the way to the end of Far Fields, onto a platform just before the Needolin door.
"Up towers spinning, near the surgeon spurned,"

Next is the north west side of Greymoor, just before entering Wisp Thicket.
"Cage of one who raged against the silken lie,"

Bottom right of Slab, head east from the bellway.
"Fell heart of frost, who soars on high,"

Climb all the way to the top of Mount Fay. This is much easier than the first time, since you can make use of the double jump to skip certain sections. Mister Mushroom is out of the ground this time, along with the next (and final) time you meet him.
"Past cradle's peak, last test of fitness, That the age may pass, this shroom its witness"

This one takes you to the top of the Cradle. If you haven't been there in Act 3 of Silksong already, you can reach it using Silk Soar in the Coral Chambers, right of the entrance to Cog Core. Where you fought the regular final boss, you can use Silk Soar again to reach a small cave in the roof. This leads to a relatively long platforming section, featuring a lot of Clawline jumps.
At the top of this, you'll find Mister Mushroom in all his strange glory for the last time. After you finish talking with him, he'll fly away. If you head upwards, you'll pop out on the desolate surface. Make sure to kill a bunch of the bugs nearby for your Journal, then head right.
At the far right, you'll find the Nameless Town. You can use Needolin at the end for some extra lore, which also causes the Surface Memento housing item to drop. After this, you can head left over the spikes to reach a shortcut back down.
While the Wish is now over, there is one final part to all this. Once you go and defeat the true final boss, everything will play out like normal. However, there's a small bonus scene right after featuring Mister Mushroom. This also unlocks the Passing of the Age achievement.
That's all for this strange Wish in Hollow Knight: Silksong! Make sure to check out more of our guides for the game below.