The Grimm Troupe is a content expansion for Hollow Knight that is well hidden and easy to miss. Follow the steps below to unlock the Grimm Troupe.
How to unlock the Grimm Troupe?
Start at the Green Path Stag station and make your way into the Howling Cliffs.
Following the map and you will come across a chest that you can jump into
Continue into the Howling Cliffs and look for two breakable walls in the cliff
There is a large bug laying on the floor at the end of a hallway. Dream Nail the bug and head one room to the left.
Here you will need to attack the fireplace to light the fire to start the Grimm Troupe Ritual
Now head back to Dirtmouth to find the Grimm Toupe has moved in.
Grimm will give you the Grimm Child Charm and task you with hunting down three flames. This will power up the Grimm Child and allow you to fight Grimm. Grimm is a very tough boss but predictable once you learn the moves. Good luck with the fight!