Greetings Fellowbeings!

I have been planning a Campaign that involves the players being somewhere between frontier trappers and treasure liberators.
The setting is an alchemy filled late 19th century Steampunk stuck in the middle of a massive swamp caused by Malfunctioning Magical Machines.

Part of this could involve the hunting of Magical Creatures/Escaped Experiments/Unreasonably-Large-Animals.

So I whipped up some rules in case they wanted to harvest more than their next meal from what they killed.

But I didn't want elaborate tables and being a fan of math this is what I came up with.

Difficulty based on Silhouette

Survival or Knowledge(Nature) for Mundane components- horns, claws, teeth, etc.

Alchemy or Knowledge(Arcane) for magical components- Flight Bladders, Frost Glands, etc.

Creatures can modify rewards based on how common or rare they are.
Magical Components are worth more

Hides, Pelts, Trophies, and meat can be sold if the right Industries are nearby.
Tanners for hides and pelts. They give bonuses for Unique patterns.
Taxidermies for trophies. Where bigger gives better Rewards.
Butchers can cure, prepare, and better distribute meat.

Each success increases the amount of parts harvested
Each advantage increases the quality of the parts
Failures signifies a botch of the harvesting
Disadvantage/threat could mean parasites or harm to the harvester

These rules are meant to be used in conjunction with resource and encumbrance tracking

Questions:
What are your thoughts on this?
How much should each success be worth?
Should negotiation checks be applied afterwards?
Are there any ways this was done better?

There's a book about this (though for D&D) on Drive Thru. It can likely prove helpful though. There's more to consider than just Silhouette though. Perhaps power levels could be a good gauge for difficulty.

Don't try and come up with some HUGE list though. Just that YOU as the GM knows what creatures will be in an adventure, so come up with these things for just those creatures at that time. Keep records of it though, so you can be consistent.

As the referee you make a list of creatures the PCs are about to meet and their useful parts. Example below. I'm just throwing in random stuff and prices I have no idea what it should actually be set as:

CHIMERA

Harvest Difficulty : 3 (based on silhouette?)

Knowledge Difficulty : 3 (based on how rare the creature is?)

Harvestable Parts :

• Lion Fangs (4) 10sp each. Enc 0. Ornamental value only. Survival to Harvest.
• Hide (4) 20sp each. Enc 3 each. Bonus for leather armors. Survival to Harvest.
• Goat Horns (2) 5sp each. Enc 1 each. Known to be ground and used in arcane Alchemy. Alchemy to Harvest.
• Snake Fangs (2) `10sp each. Enc 0. Ornamental value only. Survival to Harvest.
• Poison Glands (2) 50sp each. Enc 1. Used in highly poisonous toxin. Upgrade when harvesting due to its dangers in handling. Alchemy to Harvest.

Then, use the appropriate Knowledge skill to determine what is useful. Example : the PCs just defeated a magical creature (this Chimera) they've never harvested before. A PC rolls Knowledge (arcane) since it's a magical creature. Each success identifies something that can be harvested from your list. Check those off on your harvesting list. Perhaps pick the ones that are obvious (hide, horns) or noted by the PCs (hey, take a look at those snake fangs!) first. Future Knowledge rolls of Chimera's should reveal new items not yet identified. Advantages can give bonus on the next harvesting roll (1 bonus per 2?) involving that creature.

Next comes the actual harvesting roll. Start with the base difficulty. Time since the creature was killed could add setback. If the creature was brutalized greatly when it was killed, give an automatic 1 failure since parts may have been destroyed. Roll an action for each part attempting to harvest using the skill indicated in your creature harvesting list (Survival or Alchemy). Each Success gives 1 part of the type harvesting. Example : The PCs identified the Poison Gland and Hide as useful during the Knowledge (arcane) action of the Chimera. They go to work. Using Survival 3 diffuclty, 2 successes are rolled for the hide, and 2 parts are successfully obtained. The rest of it is ruined due to the damage during battle or perhaps the survivalist's shoddy work. The master alchemist then goes for the poison glands. That's 2 purples and 1 red due to the danger of the gland. A despair could result in the alchemist being poisoned. A master at his trade, he rolls 3 successes. There's only 2 glands, so he gets the maximum of 2 parts.

.....and I just re-read and noted you didn't want tables. 😐 Still, I kinda like this could be something I flesh out later if I have players who start considering harvesting.

In the Terrinoth Treasures series of titles on DTRPG.com, I typically have some kind of ingredients like this as components for making magical items. Might help give some ideas.