I love Cricket and Moon too! I wish we’d gotten to see more of Cricket’s pov especially, it’s been awhile since I’ve read book 12 but I remember I really liked reading about how she interacted with other characters.
I LOOOVE a villain who’s fun while also being intimidating so Scarlet has always been in my top 5. Despite only being important for one book (lol) Snowfall is also definitely up there. I remember being annoyed at first that the penultimate book of arc 3 would be spent on a character who had almost nothing to do with the Pantala plot, but I ended up really enjoying reading about her development (I’m not a huge fan of book 14 overall though) (also side tangent the Jerboa/Jerboa II vision freaked me out when I first read it, what a haunting concept). Last one that comes to mind is Glory. When I first read WoF as a little kid, I don’t think I fully grasped what her character was about but after rereading arc 1 recently, I actually related to her a lot in some ways. She says something in book 1 along the lines of “there’s no reason to try proving myself to someone who already sees me as inherently lesser for being a RainWing” and I was surprised a kids book tackled a topic that’s past Level 1 of Don’t Be Racist. You’re right, Glory from best-selling children’s series Wings of Fire, there’s no point in pandering to people who look down on you for a part of your identity that you can’t change because in the end, even if they tell you that you’re “One Of The Good Ones”, they will never see you as an equal.