We've been talking a little bit about this concept before, but let me take another approach.
As a unique mechanic we could introduce ailments that the player can contract from interacting carelessly with the world.
Perhaps not directly from just walking about, but perhaps from things like mob attacks. Imagine a melee attack from a swamp hag or peat mummy could have a slight change of giving the player the ailment 'Bite Wound' or 'Cut'.
The ailment wouldn't do much initially, but when it's ignored for too long it could develop into something serious.
Take the 'Bite Wound' for example. It could develop like this:

• Bite Wound
• Inflamed Bite Wound
• Infected Bite Wound
• Rotting Wound

Each stage would cause more severe penalties for the player, such as reduction of health regen, slowness, nausea, increased decay rate, blindness, and perhaps new effects.
The way an ailment develops into the next stage could be done through a value number that slowly increases over time but also has higher increase rates under certain circumsances, like having low decay, being in the water, being hungry, or being hit.

Examples of ailments and how to contract them:

• Bite Wound > melee attack from a number of mobs
• Cut > Crypt Crawlers using swords/axes
• Burn > Fire and fire based attacks
• Rash > taking too much damage from nettles (?)

Perhaps some made up diseases could be added to give more unique effects to certain mobs.

How to cure yourself? This is where the Apothecary comes in. A new crafting station where the player can use ground items to make specific salves, bandages, and other healing items (herbal tea?), as well as items that temporarily halt ailment development or prevent contracting ailments (though this could be another use for the Thoughskin Elixir).

All in all this could create some new and interesting situations where a the fight isn't necessarily over after killing your opponents. It would allow for some unique effects to mobs giving more variety to combat.
It also gives ground items more uses rather than being an intermediate state for getting aspects from ingredients.

The mechanic should definitely be optional through the config thouggh, and it shouldn;t become a huge burden that happens all the time, rather something that can happen occasionally.

maybe infected wounds could inflict diseases, with different biomes having different diseases to deal with.

Count me in for the made up diseases. I agree it would make for some really interresting survival mechanics and helps make mobs feel more "unique" as you put it.

"Hag Blight": causes fungus to grow on you body, inflicting random slowness and mining fatigue due to the heavy fungus

"Hag Blight": causes fungus to grow on you body, inflicting random slowness and mining fatigue due to the heavy fungus

Oh yeah, and having visual indicators would be really great. Imagine having the same fungus as the swamp hags!