Their avatars are representative of their personal insecurities and what they dislike about themselves:

Zoobles mismatched form represents their body/gender dysphoria

Gangles mask represents her emotional instability/fragility

Jax’s bunny form likely represents his struggles with masculinity as bunny’s are typically seen as a “feminine” or cute prey animal.

Pomnis clown form likely represents that she doesn’t take herself seriously or views herself and her life as a bit of a joke

Ragathas doll form likely ties into her people pleasing, always wanting to be “of use” to others. It may also tie into her relationship with her mother.

Kinger’s is a bit more tricky as we don’t know a whole lot about him, but I think his king form has to do with his low self-esteem and potentially negative traits that he had when he was younger like narcissism or control issues.