The vibe. xD But also body/face shape and colors. I switched species with my main OCs and oh boy, one looked so weird as normal human. So for him it's definitely color and traits. ^^

The right vibe can be so important! Am I vibing with this element or not and so on. I kinda love how a few people mentioned the importance of the face/body shapes. The silhouette is often forgotten, but it can tell already so much about the personality. And yes sometimes a species swap is THE thing👀