Ok so here is my thread on my theory for the Ashfur imposter.

Heads up Spoilers for a Broken Code including a Veil of Shadows.

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So at this point a lot more small hints are pointing towards the fact that Ashfur is the one behing Bramblestar's possession (1)

Especially with the cliff hanger in Veil of Shadows, with Bramblefake and extremely grieving over Squirrelflights "death" as well as telling her that "I came back for you" it also seems painfully obvious that when we got the eye color of the posseser being dark blue (2

However, these is another possibility of two spirits controlling Bramblestar's body. And this is extremely possible. Here is why.

Even though Ashfur as some time of motivation, even before he was not clever enough to even think of a plan like this. At times (3)

Bramblefake seems to be completely different. One of the things that really stands out to me is shortly after Twigbranch is rejected into coming back and a large group is exiled, Bristlefrost goes to talk to Bramble. Only to find him talking and arguing...with himself (4)

"I'll make them pay for what they did to me, I'll make them all pay"

Ashfur has nothing to be mad at, for the most part Starclan don't tend to feel emotions of intense anger or revenge, Ashfur did have a reason to seek revenge against Bramblestar but not and Thunderclan (3)

The one thing that really got me waz the fact that Bramblestar was trapped in Dark Forest. That was a big red flag to me. Ashfur, was just seen a few moons ago in Starclan. (Before the possession), He wouldnt have any knowledge of how to do anything in the DF (4)

But Cats that have lived these for moons, would have.

Falling back to our master mind, i truly do believe that it may be Mapleshade. Here is why.

Hawkfrost, as much as I belive he would have potential, he was killed, while I do wish those cats could be brought back (5)

I dont belive they would choose Hawkfrost. Nor do I belive its Sol, as while he did vow to make the clans pay, I do not belive he had any belief in Dark Forest or Starclan, so if he had passed away he would not have ended up in the Clans version of Hell (6)

Darktail is also a very strong possiblity he may have ended up in dark forest and was also described of having "Blue eyes" which would he his reason to push the for the clans to be destroyed. But this seems more reasonable if he pushed for a possession, in Windclan or Shadow (7)

Mapleshade had the BIGGEST reason to have a grudge against ThunderClan, in the Last Hope they made it really clear that she got free. She has always had a grudge against Thunderclan. And if she knew about Ashfurs love for Squirrelflight (8)

She very well could have convinced him to help her trap Starclan, in exchange of getting a second chance to live a new life with Squirrel. Especially if Ash saw Squirrel truely debating about going back to Bramblestar or not in the last book. He may have seen her as unhappy. (9)

It would explain how he was genuinely feeling grief and sadness when Squirrelflight died. Darkforest cats have been explained as not feelinf Such love, or grief. It would also explain such quick mood changes (10)

From greiving over her death (Ash) too using it as an example about the Code (Maple)

One other thing that stood out to me is the name of this Arch. The Broken Code. Darktail, Sol and Hawkfrost didnt care for the code. But Mapleshade had a reason to be. (11)

She was exiled from her own clan due to Breaking the Code. Which would explain why ahe insists on kicking everyone out. She wants everyone to suffer they way she did when she broke the code. She doesnt think its fair that no one paid for their crimes like she did. (12)

I only think its fitting that someone who wants to punish the clans with the code, is one of the cats that was effected the most by the code.

Anyway thats my theory. Props if u read the whole thread