Look, you might think that it's obvious that Brisk or Sleet did it, but think about it, Blossom was the first to say that Ghost did it, shortly followed by Ginseng supporting her. Pebble might have also just drowned, after a fight with another creature, such as Brawnshanks' monkeys.

Obviously Lychee. The dude pops into the story out of nowhere with no known backstory. Perfect candidate to be the murderer. Plus out of all the pandas its pebble that dies. PEBBLE. And sure you may think,''of course its Pebble, he is a close character to Rain so it makes narrative sense that he dies". But Peony could have also been an option and no longer serves the plot since she is barely relevant in Dark Sun. So why did Pebble die for the narrative instead of Peony? Becuase he was also part of the romance plot with Rain. Am I saying that Lychee went out of his way to specifically kill Pebble just because he was the 'other'? No, but I can imagine a scenario where Pebble confronted Lychee because of the romance plot which created the opportunity for Lychee to kill him out of convenience. Its Lychee, I bet my money on him.

All of the above except for natural causes/disaster and Ghost himself.

Obviously Lychee. The dude pops into the story out of nowhere with no known backstory. Perfect candidate to be the murderer.

Agreed, it’s a common trope for a character who randomly appears and is close to one of the main protagonists to secretly be a bad guy. Though I think it’s more likely for Lychee to be the spy and not necessarily the murderer, since Crookedclaw said there was an ally at the Prosperhill, “ally” singular, not plural. If the supposed ally were Blossom and Ginseng then Crookedclaw would likely have said “allies” instead. Or maybe I’m just looking too much into it, idk.

No, I agree. I don't think Ginseng and Blossom are with the monkeys. Even though they are a unit, they are two characters, not one. But the narrative heavily implies that they are up to something. My guess is that Lychee is the ally and Blossom and Ginseng are his cronies. The reason why is that despite not working for monkeys, they fell in line with the leopard attack, which was planned by monkeys. So I assume they work for Lychee instead of the monkeys. And Lychee is the ally.

While I do think that Lycee may be another own of Crookedclaw's spies, I think it's more likely that Bloosom/Gingseng and/or Brisk & Sleet are at fault.

@Daisy Aipom speaking of Phony Friend tropes, The Warriors Arc, A Starless Clan is revealed to have implanted a "So-Called" ally to one of the protagonists in the latest installment. I'm not naming names as the character I'm referring to contains major spoilers for the Starless Clan Arc.