It can be from scratch, and it can even be other creatures. However they live mostly on dragon (the Olfur’Yehkshir don’t need to eat as often), they can feed on beasts or smaller creatures, even to gain their disguises, but they seem to favor dragons. Ether for usefulness or taste is unknown. Eating them and gaining the raw material itself is just quicker; Making their mimicked form more accurate after not only spying on them, but getting the real thing to copy. That way scars, speech patterns, quirks and whatnot can be accurate enough to lure pray away long enough to eat and whatnot~
~Weird Hyenas
Weirdlanders 