Finback - 4/10
I really enjoy the idea behind the name, and I enjoy the story of the cat itself. I cannot, however, ever see the suffix 'back' being used. What also gets me is that a mother does not know how her kit will swim when she names it, however I could see a mother in a swimming/water Clan naming her kit something like that just on principle, so that part slides for me. It just flows very weirdly as a name as well; it doesn't seem like a warrior name to me. I'd like to think there are other suffixes that would both flow better and make more sense as a suffix in general; personally, I would use something like -splash, -stream and maybe play around with different prefixes to make it flow better. But again, I guess that might come down to personal preference and, after all, it is your character and not mine.
Copperpond - 8/10
Ok, I really adore this name a lot. The only thing that docks points for me is that the alliteration might become too much, especially if this character was the main one in a story or RP. The double 'p' sound can get annoying, at least to me. Personally, I like having the metal as a prefix - or if you were iffy on it you could always have him come from a different background than from the Clans. I mean, if you think on it, Firestar's first name was "Rusty," and none of the Clan cats that knew him as Rusty made fun of him for having a weird name. I'd like to think if they understood rust, they would understand a couple of metals?
Plumetail - 7/10
I am not a huge fan of the prefix. I think it's just that when I think of 'plume,' I see something both soft (which is why I do like it for this cat) as well as something colorful because I like colorful birds, so in that sense I don't quite like it for a white cat. But then again, I do know that there are plenty of white birds so it makes sense.
Lotusheart - 10/10
I adore this name a lot! It sounds awesome, suits the cat really well, and I love her story. I like how you combined an uncommon prefix with a pretty commonly used suffix, but it makes a unique cat!
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Very non-traditional namer here, so I apologize for the names if you do prefer traditional ones x)
Rainshadow [a smaller black and white tom with dark amber eyes. He is charismatic, yet he uses his charisma to manipulate others into benefiting himself and only himself. As an apprentice, he cared a lot about his Clan, but due to a very bad leader and deputy combination, and being the apprentice of the leader, Rainshadow learned that he could only look out for himself and that he didn't much care for the Clan anymore - especially because his own family didn't believe the mistreatment he was getting from the leader and the deputy].
Lightflame - [a white tom with light ginger tabby patches on his fur. He has soft green eyes. Lightflame is the deputy of his Clan, and he is very caring for every single cat in his Clan. He has a lot of passion to better the Clan and get rid of the problems, ever since he was a kit.]
Cedarsmoke - [a dusky gray tom with slightly longer fur and dark green eyes. He is gruff and seems harsh on the outside, which also makes him seem way older than he actually is. Truthfully, he has a soft heart but doesn't like to show it - his stubborness and pride keeps him from showing pretty much any emotion. Instead, he turns his attention to hunting and stealth techniques.]