Complex sentence: Here elves are most often attested in Old English glosses which translate Latin words for nymphs and in medical texts, which attest to elves afflicting humans and livestock with illnesses: apparently mostly sharp, internal pains and mental disorders.
Split into simpler sentences: Here elves are most often attested in Old English glosses which translate Latin words for nymphs. Conveying an Old English negativity toward the elves, medical texts attest to elves afflicting humans and livestock with illnesses: apparently mostly sharp, internal pains and mental disorders.