In the end cards, Callum asks Rayla not to turn into the moon (since Callum is voiced by the VA of Sokka and Rayla also belongs to a tribe of people that is closely tied to the moon) referencing that Water Tribe princess.https://f95zone.to/threads/four-elements-trainer-v0-9-9c-mity.730/post-7604998
I beat you to it!
I missed the Avatar reference. What is it?