A Troll's Liver plus a Troll Culture
Guideline Purchasing Price: 300GP
The Troll's Liver needs to be preserved in a Troll Culture to prevent it regenerating into a Troll (though constantly doing it Damage can also work). A Troll Culture is a Potion bottle containing a mild Acid solution (though Alchemists do not generally admit to this). Its Guideline Purchasing Price is 1GP, but most Alchemists will generally charge a larger deposit (typically 10GP) refundable against the purchase of the Troll's Liver in order to encourage adventurers to consider the Troll Culture as valuable. The Troll Culture is added to the Potion Base, so is considered part of the Materials. It is not necessary to use the same Troll Culture as was used to preserve the Liver, though most Alchemists consider it safer to do so.
Only one Potion of Regeneration can be produced per Troll's Liver, as only the largest remaining part has the Regeneration Power. Attempts to cut them into two equal parts have proved unsuccessful. Note also that most of the rest of the Troll must be burned or dissolved in acid, as if the Liver is not the largest remaining part, it will not have the Regeneration Power.
Elementalist Regeneration with a Throw giving a minimum of Rate of Regeneration = 1 HP / 6 sec (i.e. any successful Throw).
Guideline Purchasing Price: 33GP
Duration (non-Extendable) is 9 + d6 min (i.e. 10-15 min)