@The Seliph-loving Gryffindor who also loves dragons and cats
Ferality is a condition in my fanfic concerning Nekomata and Manaketes.
Ferality is normally inflicted by bite, like a werewolf or vampire, but instead of just anywhere, it's in the heart. Although the bite itself is painless and doesn't cause any damage, except a streak of blood, it starts a horrific condition in the poor victim.
There are very few Nekomata and Manaketes born with ferality, Seliph being one of them. This condition only shows when the victim uses a Dragon/Beaststone to transform instead of non-combat transformation. This only affects purebloods, as far as what's currently known.
Seliph was subjected to ferality studying as a baby due to it being the safest way to look into this strange condition. However, just because he was very young and oddly weak for even a baby Nekomata, it didn't mean it was safe to be around him when he used a Beaststone. What is known is that those affected with ferality are very violent and predatory. Teen and adult ferals have even been know to eat humans. Some ferals have gone so down their dark path that they will eat humans in human form. There is a tale of a feral Manakete who killed an evil king and soon after, got her mind back to normal.
Half-bloods and humans don't suffer from these, half-bloods due to having to use a Dragon/Beaststone, humans because they can't use stones to transform at all. There is an urban legend circulating around that there is a half-blooded Nekomata who inflicted ferality upon himself. Inflicting ferality upon self is impossible, as far as studies have gone, so this is most likely just a myth to scare little kids into eating their vegetables.
Just some ideas for shifters in your stories.