Medusa/Lamia both have the same kiss attack, called Charming Kiss, where they blow hearts at you, which deal damage and can paralyze. They're pretty easy to find in Niflheim, and maybe some other places.
Edit: here's a vid of it; quality isn't that good, though: https://www.youtube.com/watch?v=mtGuvsaV2j4#t=1m00s
Edit2: Here are some better ones:
Presea gets one: https://www.youtube.com/watch?v=mjT6lgdElWU#t=8m38s
Another one: https://www.youtube.com/watch?v=ku8h8tCjgDU#t=2m39s