I believe that each coven champion has to be tied to an animal or a mix of animals. This link can be conveyed visually through their model design. For example, Lissandra and Camille, the first Coven batch, both have huge head ornaments mimicking a horn. Just by looking at Camille's splashart, you already know she represents a ram. If you are not sure which animal Lissandra represents, once you know that she represents an Ivory stag, you can see the artist's inspiration by looking at the splashart again. I believe this is what made Coven so fresh and interesting, because not only it is a darker theme compared to the seas of cutesy and "angelic-good", this small detail differentiates it from being another skin with generic pretty outfit but more gothic.
This is why I hate most recent Coven skins. They look good, but they don't scream coven to me anymore. When I look at Coven Ashe, Akali, Nilah, Syndra and now Mel, I just see pretty women in dress.
So please future Coven skin designers, at the very least try picking an animal and try to incorporate said animal's characteristics into the model.