Hollow Knight is a 2D Metroidvania platformer developed by Team Cherry. I consider the charms system, inventory system, and the maps system to be the secondary systems of Hollow Knight, while the movement and combat systems are the core systems. Without the unique movement and combat system, Hollow Knight would be a radically different game, however the removal of the charms, inventory, and maps system would represent a smaller loss, which is why I decided to label them as secondary systems.
Charms are a unique set of effects that can be given to your character as they adventure around the world that can effect and radically determine your playstyle. For example, there are charms that boost the effectiveness in spells in multiple ways, like reducing the cost to cast a spell or increasing the damage a spell inflicts. There is a charm that increases your base health, a charm that boosts your melee attack’s damage, a charm that causes you to gain Soul faster, a charm that spawns a few spiders to help you in combat, and much more. There are 40 charms in total, but all of them cannot be equipped at once.
Depending on how many charm notches you have unlocked, you are only able to equip a set of charms that can fit within the charm notch limit, and charms have different notch requirements. For example, a charm that slightly increases your melee attack range may require 2 charm notches, while a charm that moderately increases your melee attack range may require 3 charm notches.
You may choose to overcharm your character, which allows you to equip one additional charm above the charm notch limit, however your character will take double damage from all sources. Additionally, charm effects are stackable, so equipping both levels of charms for increasing melee attack range will result in a sizable melee attack range increase. Overall, charms provide players with the ability to make their own loadout that best fits with their playstyle as they adventure through the world.
The inventory system allows you to store various items with you as you collect, mainly the game’s currency, which is called Geo, unlocked upgrades, and unique items such as Pale Ore, which allows you to upgrade your nail. When exploring Hallownest, Geo that is collected is added to your inventory where it stays until it is either spent or when you die. Geo can be spent at the various vendors located around the world in exchange for upgrades, charms, and more. Unlocked upgrades will also appear in your inventory which can be selected and viewed to review your upgraded move set. Unique items such as Pale Ore, Simple Keys, Rancid Eggs, and more also appear in your inventory so that the player can see how many they have collected or how many they have left to use. The inventory system is not very interactable, for example, players are unable to rearrange or organize the items they have collected. The inventory system is mostly there just to provide players with the ability to track their items and currency.
The starter maps in each main area of Hollow Knight can be bought from an NPC. Each area’s starter map is not fully charted when you first buy it, however if you have bought the quill, by exploring new areas of the map, the map will fill itself out as you progress. The mapping system allows players to track where they have and haven’t been on the map. There are also pins that can be purchased that can be placed anywhere on the map for future reference.
Interactions between secondary systems:
While these secondary systems may seem unrelated, they interact with each other in a variety of ways. For example, the charms can be found in the world and added to your inventory through either buying them through a store or exploring uncharted areas of the map. Starter maps have to be bought and added to the inventory before they are able to be used. There are also charms that improve the inventory and map systems, such as a charm that automatically picks up Geo that drops in tough locations, or a charm that serves as a compass, marking where you are on the map when you view it. These secondary systems also interact with the core systems to make Hollow Knight a unique experience when compared to other games in the Metroidvania genre.