Metroidvania games tend to be more difficult on average than many other genres. Their core conceit revolves around surmounting once-impossible challenges by obtaining mechanics that open up portions of an interconnected world. Team Cherry's Hollow Knight is well-regarded for its challenge even among contemporaries because of its Souls-like elements, and how it builds upon the oppressive atmosphere of Hallownest with tough-as-nails bosses and tricky platforming. No doubt the upcoming Hollow Knight: Silksong will follow in its footsteps.
Basic movement and combat are taken to extremes in Hollow Knight's base game, but there are also optional challenges like the White Palace's Path of Pain or boss rushes in the Godmaster DLC to contend with. One of the biggest challenges players can tackle is Steel Soul mode, which adds permadeath that wipes out a save file ala Hardcore mode in Minecraft. Team Cherry confirmed Silksong will have "Silk Soul" mode in its 2019 announcement blog post, and while details are currently sparse there is a lot of room to improve upon Steel Soul's offerings.
How Steel Soul May Translate to Silk Soul
Hollow Knight players unlock Steel Soul mode upon beating it for the first time. As previously mentioned this adds permadeath, affecting a few facets of the game. For example, the base game features Confessor Jiji: an NPC in Dirtmouth who summons the Knight's Shade in exchange for a Rancid Egg, allowing players to recover their lost SOUL and Geo (money) without returning to their place of death. Steel Soul mode replaces them with Steel Soul Jinn, who simply trades Rancid Eggs for Geo.
That being said, the changes are not extensive. Hollow Knight in Steel Soul mode is largely the same experience, just adding the threat of a save file wipe at any given moment - with the exception of battles against Dream Bosses or in Godhome. Overcoming the challenge nets players a new main menu theme and an achievement, as well as a second achievement should they 100 percent complete a save file in Steel Soul mode.
One might assume Silk Soul mode in Hollow Knight: Silksong will fit the same mold, as Team Cherry said it will also unlock after players "conquer the game" in its announcement blog post. However, the developer does not go in-depth, only telling fans that Silk Soul is "an all-new mode that spins the game into a unique, challenging experience." That verbiage suggests changes will be more extensive than just permadeath, in which case there are a few ideas Silksong could try.
Features That Would Help Silk Soul Stand Out
Silksong was originally intended to be another DLC expansion for Hollow Knight, but Team Cherry saw its scope and decided to make a full sequel; still promising to give Hollow Knight Kickstarter backers Silksong for free. It takes antagonist-turned-ally Hornet to a new kingdom called Pharloom, and players must help Hallownest's protector escape captivity. It's set to be an inverse of the first game, with Hornet climbing to the top of Pharloom as the Knight descended into Hallownest's depths.
Between the shift in narrative and new mechanics inherent to Hornet, largely around her needle and thread, it's likely the game will not follow the same beats as its predecessor. If so, one area Silk Soul mode can excel is by changing the world map. Hollow Knight changes part-way through the main story as the Forgotten Crossroads below Dirtmouth are infected, making navigation and enemies more challenging. Assuming Silksong eschews this concept, Silk Soul mode could incorporate these into a New Game Plus-style challenge instead.
Similar game design is found all over the industry, notably in the Legend of Zelda franchise. Ocarina of Time received its Master Quest rework alongside The Wind Waker, redesigning dungeons to be more difficult. Breath of the Wild's Master Mode focuses more on enemies, making harder variants appear earlier as all foes recover health over time.
Silksong does not have to make all of these changes in Silk Soul mode, as it would become exponentially harder with permadeath. However, a Pharloom-wide New Game Plus rework would help it stand out from Steel Soul. Beyond that, limiting the resources players can collect or use would also increase the game's challenge, despite changing the requirements for 100 percent completion. For all this potential added difficulty, Team Cherry could even add a reward with in-game effects instead of just cosmetics and achievements.
Hollow Knight: Silksong is in development for PC and Switch.