Clerics using griffin feathers to cure blindness does not sound very historically authentic.
Pretty sure the Romans killed all the griffins during their occupation of the Isles, so yeah, no feathers to be found by mid-evil clerics. Also anything related to faeries after St. Patrick is horseshit since he banished them all.
Those accursed Romans!
Anyway, I made a mistake by saying that. I meant to say "medieval authentic" or whatever the advertising blurb is for
Lion & Dragon IIRC. Basically, whatever J.K. Rowling was doing by referencing her library research in her fictional books.
The issue with material components gathered from monsters is that it encourages players to think of creatures more as harvestable commodities and less as fantastical creatures. Charaters carting around bloody bags of monster bits like a World of Warcraft player, hoping a Basilisk toenail can cure someone's gout.
Which may or may not be a feature you desire in a game.
Well, players certainly aren't encouraged to think of them as fantastical
now. That was what I was originally complaining about. Players
already think of griffons in terms of whether they're a valuable mount or source of treasure and nothing else. (I find the fantastical vs natural dichotomy nonsensical anyhow. Medieval bestiaries had tons of bizarre ideas about real animals that make them feel more "fantastical" than many D&D monsters.)
Furthermore, medieval bestiaries
did describe creatures as harvestable commodities. That's pretty much a side effect of human beings thinking of the world around them in terms of utility value. That's always been the case around the world and in folklore. For example, descriptions of the manticore state that rich people in "India" would have baby manticores captured, their tails crushed, and kept as pets in choirs because of their pleasing trumpet-like voices.
It's a "damned if you do, damned if you don't" situation. Humans by nature think of everything around them, including fantastical creatures were they to exist, in terms of utility value. It may destroy the fantasy for you personally, but for me it feels more immersive because that's exactly how humans would perceive fantastical creatures if they existed. By existing in the same world as humans, they're no longer nebulously "fantastical" but concrete creatures that you can use as mounts or sources of medicinal and alchemical and magical components.
IIRC, ACKS has a section where it mentions that the party wizard can open their own dungeon to lure magical creatures in order to harvest for spell components.