The ideas you cite seem cool and not so much work. The pseudo cut-scene with the goblin’s toast to the absolute already exists, as do the potions’ effects.
Thank you, thats what i thought aswell.

Is the recipe mugwort + water or is it enough to stick the plant alone in the cauldron?
Just stick the plant into cauldron.
That Link doesn't work. It is about the Wyvern posion or something different?
Potion of poison, it gives 1d4, you can find it
inside the apothecary celar
Its odd item, since you can only drink it ... i didnt find any way to coat your weapons with it, unless its thrown and you then dip in that puddle.