Outside of Keys (used to unlock doors in dungeons) and Artifacts (unique homogeneous items used in dungeons and elsewhere to open other gates), items are classed out the following ways:
Bait -- hetero item used for Fishing. Probably just attached directly to the equipped Fishing Rod for sanity.
Tools -- unique items used for harvesting resources or doing things like Fishing.
Pack Tools -- unique items used for doing stuff with resources inside the backpack. These probably aren't indicated directly since they're stored in specific locations, attached to whatever fixture makes sense.
Weapons, Spells -- uniques used in Combat
Armor -- unique Equippable item that adds defense in Combat.
Fish, Flora, Fauna -- probably classed separately but also upcatted together
Metals -- Used for forging weapons/armor/spells/tools. IIRC, regular metals are used for tools and weapons while precious metals are used for armor and spells.
Crystals -- used for upgrading the magic backpack in various ways.
Materials -- other materials used for upgrading fixtures in the magic backpack, some of which have to be crafted from other materials (such as sand --> glass --> upgraded aquarium).
Food -- Meals made from processed fish, flora, fauna. Meals affect health, stamina, mana, regeneration of these as well as protection from environmental hazards.
Potions -- made from rare extracts of processed fish, flora, fauna, monsters. Affect every other system in the game. Like in NIFE, Potions can be variously drank, poured or flung depending on what they do specifically.
A good description of how the potions/items systems in the game work (which is kinda needed before I start fleshing them out) will come from describing the Combat system in more depth.
Combat is branched GTTian. You make choices about attacks and also choices about dodging patterns. There are a lot of differences (like an actual health system) but this is the basic gist of how it works.
Your attacks are dependent on your weapon. There are multiple weapon types, which have different attacks associated with them. You get these attacks based on what you have equipped. Some might be unavailable for whatever reason (like an enemy that's underwater might be resistant to close attacks with an axe for obvious reasons). Special attacks can also be based on combat tags (more on those in a moment), and are just available whenever those tags are true.
Enemies choose attacks randomly or possibly in a weighted way depending on tags (more on those in a moment). Enemies have multiple attacks, which deal damage and can alter combat tags. Attacks themselves have "attack tags" which can be targeted by various systems.
Enemy attacks go through your armor first, then hit your health, unless they have attacks that bypass armor of course. Armor can resist damage but can also resist, absorb or bounce back specific types of attack tags. Bounceback attacks are non-elemental (otherwise it doesn't make sense).
The element system, copied from Shatterloop, is in play here. Enemies that are elemental will absorb their element, deal 2x damage to the elements that they attack, and take 2x damage from the elements that they defend. A fire elemental for example will absorb fire damage as a form of healing, take 2x damage from earth and water attacks, and deal 2x damage to wood and ice based armors. It will also take 1/2 as much damage from ice and wood damage and deal 1/2 as much damage to water and earth armors. So pokemon rules basically. Not all enemies are elemental.
The Tag system
Tags are temporary labels that are applied to various entities in combat -- the enemy(s), you, the environment, your equipment possibly. Tags have no intrinsic effect -- they're instead things that can be targeted by your or enemy attacks.
For example, a bat enemy might have a "fly high" move. If they perform it, it adds a "high flying" tag to themselves. Because of how this is set up, they're immune to all close-range attacks by you. They can then also perform the "swoop" attack, which in addition to dealing damage will remove the "high flying" tag.
Tags have more useful names and are always visible. By fighting an enemy a few times you can unlock its Bestiary entry which will actually spell out exactly what its programming says in a parseable way so you have a better idea what to do if you encounter it again. Bosses, meanwhile, will unlock the Bestiary entry after one defeat.
Environmental Tags
Some environments can apply tags to the battle prior to the fight. Or with a chance. While this is generally environmental tags, it can also apply enemy-specific or you-specific tags (generally with a chance) provided that the enemy actually has some programming that hooks into it. An area full of updrafts for example might make a bat start out with the "high flying" tag.
Enemy spawning
Enemies spawn exclusively in Caves and Dungeons. These each have specific spawn rate variables that set how likely one is to spawn, how often and possibly where. Enemies will spawn in completely random rooms based on the game seed, but this is distributed rather than completely random.
If an enemy(s) is in a room, you can't interact with anything in the room (including other passages) until you defeat the enemy(s). Once defeated, they'll stay dead but will respawn according to the cooldown stat (which is probably location-specific). The time system here is based on movement to different rooms in the game actual time passing. This allows a form of farming, which is useful for gathering their materials for use in Potions.
If you die, you restart in the Chimera chamber in the center of the world -- there's a good Lore explanation for this. It's pretty annoying if you're pretty far into a dungeon, so don't die.
Geomes
Geomes will occasionally spawn in the overworld, and are more likely to do so nearer to their base of operations in the Lava Sea. These are very tough fights, so you're probably best off rerouting around them with the open world nature of the game. Given enough time however they will move elsewhere, completely randomly due to their eldritch nature.
Flora and Fauna are randomly distributed in the areas that they can spawn in. Some locations might always have them -- for example the Duck Pond in the Owl Province will always contain Ducks. They aren't necessarily exclusive to the overworld -- mushrooms for example will grow in Caves, as will Bat fauna.
When you collect a Flora item, you can't collect it again until its cooldown timer expires. It's on the same system as enemy respawning.
Flora is obtained either via a Scythe (for brush, herbs, etc) or an Axe (for trees). They take some amount of real-world time. This can be upgraded if the tool is better, which can also up its yield or add favorable properties to the item that becomes important once you process it. Tools do however tend to target specific types of flora.
Fauna operate similarly, however it applies whether you kill them or they flee. Worth noting, if you attack a fauna it will cause all the fauna of the same type in the room to flee.
Materials
Materials are on the same system as flora. They use tools such as the Shovel and Pickaxe in a similar way to Scythes/Axes.
Fauna Collection
To collect a fauna, you have to hit it with an arrow successfully. Arrows are a consumable item that can be crafted with materials found in the world. There's some accuracy there, but different bows can have bonuses on different types of fauna, or you can use the potion pouring system to temporarily enhance bows in various ways. Additionally, these different bows/potion effects will affect yield and deeper properties once the item is processed. They can also have an effect on animals of the same type fleeing.
Whether you successfully collect a fauna or not, all fauna of the same type in the area will flee and will only respawn after their cooldown timer.
Extensive Handcrafting
All flora and fauna are handcrafted, as are the resources taken from them.
Fishing requires Bait, a material found in dirt piles, etc and on that system. Bait is somewhat rare, so better yield shovels, etc are essential for gathering large amounts of it.
Fishing can only be done in watery locations. These are found in the overworld, sometimes in caves/dungeons, and occasionally in towns/POIs. There's a small pool in the Chimera Castle for example.
Each pool has a fixed handcrafted amount of different types of fish. They will respawn after 24 real world hours after you've caught your first fish. Different fish have different priorities on their weights, but if you exhaust the pool you will definitely get the harder fish eventually. You get to see how many fish are left and when the rest will respawn. Each pool is on a different timer, which is based on the first fish you've successfully caught. So you can come back in 12 hours and fish more and just have to wait another 12 for them to all respawn.
Fish can be easier or harder to catch, and this number can be improved with better Fishing Rods -- they target specific fish tags, which are always visible somewhere in this menu. Fishing rods may also alter the likelihood of using Bait on certain fish tags, or increase yield or other useful downstream properties.
Fishing takes actual time, generally more than other resource collection minigames, and this can be improved with better Fishing Rods or particularly pourer potions.
Spells can be created with a region's precious metal resource. You have to go to the specific vendor that makes the spell. There isn't enough precious metal to craft every spell in a region, and besides, it overlaps with armor crafting as well, so you have to make choices.
Spells are used inside combat and do various things -- dealing damage, altering tags, etc. They cost Mana, which regenerates over the course of a battle rather than in real time.
Stamina
All moves consume some amount of stamina. The more stamina you have (or the less attacks/dodges cost), the more actions you can do on your turn in combat. Special moves tend to use considerably more, and you may even be locked out of them if your max stamina isn't high enough.
Changing your equipment mid-battle costs a lot of stamina. Consuming Food and potions also uses some fixed amount of stamina.
Upgrading
Mana, Stamina and Health can be upgraded with a Limited Resource known as Vitality Orbs -- you have to choose what they target specifically. This happens at the Mirror fixture in your magic backpack, and you can also adjust the distribution of these stats therein, provided you've unlocked that upgrade with Crystals.
The stats and their regeneration and their recovery can also be improved with various types of food. Food may also have deleterious effects in addition to its beneficial ones, depending on the properties of the food items used as ingredients in the recipe.
Chimera
A fourth stat, Chimera, can also be assigned with Vitality Orbs. This allows you to fuse usable items together, combining their properties. They still take up the same amount of space, however. Each fusion costs 1 chimera, and unfusing regains that chimera. Chimera can't be targeted with Potions or other effects.
Fusing and Unfusing happens only at the Chimera Altar in the Chimera Castle.
Fusing consumables will actually add their properties together, allowing you to make things like super-powered potions which would otherwise just be updates to their properties. When consumed, you regain all the Chimera you spent. The downside is this leaves you less Chimera for fused weapons/armor/spells/tools which are very useful despite not summing their stats together. Additionally, having more Chimera means less Stamina/Health/Mana.
Some additional caveats to this system:
With non-consumables, you get to pick between the two values which one you want. With traits, you can also pick both (for example elements). Generally you're going to want to maximize values, but there might be conditions where you won't want to.
Precious metals -- used for making spells and armor
Crystals -- used for upgrading your magic backpack
Vitality Orbs -- used for upgrading mana, health, stamina, and chimera.
While there's a decent amount of Vitality Orbs and enough Crystals in the world to unlock everything, Metals and Precious Metals are limited by design -- you won't be able to forge everything you potentially can; you'll need to choose.
Limited resources are scattered around the world:
Each quest gives you a random limited resource unless it gives you a Unique item instead -- Unique items are Tools/Weapons/Armor/etc and are handcrafted to belong to that particular quest.
They can be found in caves and dungeons randomly.
They can be found at Shops, where they cost money.
Each region always has the same amount of each Limited Resource -- this does not change between game seeds.
Metals, Precious Metals and Crystals are region-specific. With Crystals this doesn't matter, since magic backpacks can be done with any kind of crystal, however items are forged with specific metals and precious metals. The naming there is based on the ones in Shatterloop, except with Houtum renamed to something else.
Shops allow you to sell resources of their specific type for money, and to buy non-rare resources as well. They have a limited stock, and their wares change and restock every 24 hours in real time. They do however have infinite money.
General shops will buy and sell anything (selling non-rare stuff here too), however you get 1/2 as much as you'd get by going to the specialized vendor. They might be more convenient if you're doing a lot of farming however. Towns will always have General Shops, but specialized vendors are more scattered.
Curio Shops will sell Limited Resources and Uniques, and literally anything else including powerful potions or rare stuff. Their wares change every 24 hours and outside of the fixed Limited Resources are not handcrafted. You can get some pretty weird stuff sometimes. There is probably a heck of a lot of markup though. Also I might scrap that mechanic. If they sell Uniques, this is similarly handcrafted.
Anything sold is gone forever. As a result you can't sell non-consumable Uniques (weapons/tools/etc). Nor can you sell Limited Resources.
Instead of both Metals and Precious Metals, there is instead just the Metals. Still a Limited Resource.
Weapons, Tools and Armor are crafted with the Metal as well as a diaspora of PCGS materials. World materials are always represented, but flora/fauna/fish/monster ingredients can be represented as well. These are no longer handcrafted, and the recipes are sold in Shops, with the variety dictated by the game seed. However, elemental weapons and elemental armor are always represented in the correct region. The other properties are totally random, and this alters their price accordingly. The actual item properties in question are what is seeded -- so the recipe will always be the same for the exact same item.
Spells/Potions Changes
Potion ingredients/effects change from world seed to world seed. There should at least be distribution happening, but it's no longer region-specific. So you will most likely need to go to multiple regions to track certain types of Potions down.
Spells are now literally Potions, which are already affecting every system in the game. The way this now works, there are a Limited amount of Crystals in the game. Crystals can be spent to turn a Potion into a Spell -- this allows you to use the effect repeatedly but costs Mana.
With more Crystals, a Spell that targets you or an item you have can be turned into a permanent Enchantment. Enchantments don't cost Mana and their effects are permanent.
Spells and Enchantments can't be chimera'd, however the potions that compose them can be. Turning these into Spells or Enchantments requires the combined amount of crystals, however.
Rerouting
Crystals and Metal forms aren't permanent. A Magic Backpack process will pull them away from active forms so you can reshape them. The downside is, you lose all other materials that were used -- Spells for example will lose the Potion, while Weapons will lose the other materials that went into crafting the Weapon. Another downside is that this process consumes Fuel.
This does at least encourage more experimentation. You still can't do everything with the metals and crystals you find.
Conclusion
Obviously, this makes the game significantly more Shatterloopian. However it also means that all I have to do when building out the world is setting what things are and where they are, and the PCGS system handles the rest. This is definitely preferable on my end, and the PGCS makes the game more explorative including for me.
The Magic Backpack is essentially a portable Base. It also stores all your items, with infinite storage capacity (anything else would be overly annoying). It is subdivided into Rooms, which can hold Fixtures. Fixtures do various things, and have to be crafted via the PGCS in generally a region-specific way (like the Fletcher is made from materials found in the Wood region).
The Magic Backpack can be used anywhere outside of Combat or specific areas that have Wards against it (might never happen, but you never know).
Any Fixture that does something (like a Crafting task) takes real time and costs Fuel. This can be sped up by adding more fuel, or the rate can be altered with Pour Potions that have that kind of effect.
Fuel Mechanics
Fuel mechanics are entirely Shatterloopian. Fuel can be obtained by adding plant materials (or fuels) to a Boiler fixture. Different Fuels can be refined from various other materials with a fuel cost of its own to get to higher tiers of fuel, which is important for higher-tier processes. Fuel refinery recipes are however on the PGCS -- you don't just start out being able to make neutronium (or whatever). I also think a 10x magnitude shift is too high, maybe 4-5x would work better.
Labs
Each Room has a Lab Fixture in it which lists the unused research and the materials needed to advance.
Research doesn't take time or cost Fuel; it's entirely dependent on the Materials you gather instead.
