Highly-regarded Aussie metroidvania title Hollow Knight is getting a second free content pack this Halloween.

The Grimm Troupe contains a new major quest and boss fights, alongside new Charms, enemies, friends, music, and more.

"Light the Nightmare Lantern and summon the Grimm Troupe to Hallownest, if you dare!" its pitch reads.

"Take part in a twisted ritual that stretches the breadth of the kingdom and bestows the player with a powerful new ally."

In a blog post, developer Team Cherry also announced that Hollow Knight has sold more than 555,000 copies to date across PC, Mac and Linux.

"For two people sitting in a tiny office in Adelaide, that’s beyond humbling," said Team Cherry.

"To all of you who’ve played, purchased or championed the game: Thank you. Thank you. Thank you!"

The game is coming to Switch (with The Grimm Troupe included), but Team Cherry is reluctant to give a release date.

"As agonising as that is, we can say that things are pulling together (frame-rate is getting the thumbs up!), but there’re still a few more hurdles to clear before we can give you a release date that we’re 100% confident we’ll hit."