Yesssss. Frank had so much potential and I feel like some of it carried through but also the ball dropped on him a little:
HE DID NOT GET SKINNY. He just got a little taller because size difference slaps and also I think it's funny that he was already pretty fucking tall and yet Mars was like "you're too short, here's a couple more inches pipsqueak", like bro
Deals with depersonalization - the more he shapeshifts, the more he starts to lose touch with his humanity. Eventually he just can't recognize himself in the mirror, his body feels weird, like a skinsuit he's stuck in, something someone zipped over his head and no matter how hard he tries he can't reach the zipper to get out
When he's really going through it, he shapeshifts into whatever animal (or animal combo) makes him feel a little more settled. But even as an animal, he doesn't always feel there. It's a permanent unsettlement now, and he just has to make the changes to get through it
He can mix-and-match animal traits. I know it's canon that he can't but like, idc, i wrote it in a fic and I think it fits his depersonalization struggles, like he'll fuck with as many body parts, traits, etc, to get something that feels okay and the output sometimes isn't a bear, but a bear with tiger legs and a lizard tail and so on
He doesn't get along with the Ares cabin. they're too rough and tumble, Mars is more disciplined than that so he finds their anger and violence unnecessary and sometimes distasteful
Despite that, he gets angry pretty easily. However, he dislikes his own anger so he sort of separates it from himself and, as such, doesn't always recognize when he is angry (I think Jason is a little similar sometimes). Like Jason, as well, he tends to see his anger as more of a rational thing rather than an emotional response
He speaks French better than he speaks Chinese
He's pretty introverted and doesn't really enjoy socializing
He can play the violin! His grandmother put him in lessons when he was very young. He's rusty as he hasn't played in a long time, since he quit a year or two before he left for Camp Jupiter. He's always been a big strong boy so his grandmother thought the violin would help him learn to be more delicate and aware of his movements
The only person he's ever really been attracted to is Hazel. He's probably gray-aroace, but he doesn't care enough to think further on it. He knows he likes Hazel and he doesn't really need to look at it any more than that
He and Nico play Mythomagic with each other. Not on a regular basis but whenever one of them gets a new pack or if Nico is hanging around for a little longer than a couple days. They both agree that the games are just for fun but they still get competitive about winning anyway and are 100% keeping score in their heads