I think the slinker is the chest gem in the temple fusion, not amethyst. (assuming ronaldo’s drawing/picture isn’t 100% accurate)
The chest gem on the temple is ovular and round, like the slinker’s gem and not like amethyst’s gem.
The temple is skinnier than amethyst, rose, pearl, and garnet would be combined. (think of alexandrite + rose).
the temple’s mouth and mask dont have teeth like amethyst’s fusions (alexandrite, sugilite) from what is seen.
the temple appears to have protected a portion of the land from a blast, possibly the corruption song. If it was the corruption song, then amethyst most likely wouldn’t have been with the other gems during said song.
the temple’s weapon appears to be a sword. the sword resembles garnet’s gauntlets at the hilt and pearl’s spear, but only slightly resembles amethyst’s whip.
human characters (such as ronaldo and steven) don’t know when or how the temple was made, implying it wasn’t recorded historically.
Ronaldo’s predictions are often slightly off or even wrong sometimes. The temple gem might not resemble his drawing, meaning it might not resemble amethyst.
Ronaldo states in his journal entry that There’s “probably no connection” between the temple and the giant woman who picked up dewey’s ancestor. If a lot of Ronaldo’s crazier, less focused on theories end up being true (the zoo, hollowing out the earth), then that means the giant fusion seen in colonial times might have existed after the temple was made, not before.
The fusion shown in Jamie's play interpretation does not resemble the temple closely.
The slinker is the first and only corrupted gem in the temple that isn’t bubbled. When they discover it isn’t bubbled, they don’t wonder why or freak out, like they did with peridot and the gem shards.
Amethyst calls the slinker “MY monster”, and treats it like a metaphor for her emotional stress, as if she sees it as more than a monster, and seeing it reminds her of her bottled up feelings.
The slinker’s “petals” and the ends of it’s tendrils resemble the mask of the temple, and it’s tendrils resemble the temple’s lanky body and curly hair.
The temple has elements that resemble amethyst, such as her poofy hair, a gem on her chest, and a second face like amethyst’s fusion as alexandrite.
the hilt of her sword resembles the hilt of amethyst’s whip.
characters in the series imply that the temple is based on a fusion that saved buck dewey’s ancestor in colonial times, a time where amethyst most likely existed.
Ronaldo, who’s predictions have been right on occasion, made a drawing of the temple that makes it look like amethyst. (the hair and skin color, her lips, her gem color, etc.)
The pilot shows the gem on the temple as being purple.
I don’t think it’s amethyst in that fusion. I think the crewniverse are trying to thow us off with the VERY amethyst-esque picture Ronaldo drew. I mean, it has her hair color, skin color, gem color, shirt color, her lips, her eyes, and her body shape (at least, more so than the actual temple). I think they made this pic so people would assume “If Ronaldo has been right so many times before, and it looks like amethyst in his picture, then why wouldn’t amethyst be in the fusion?”, only to be surprised when it turns out otherwise. Ronaldo probably thinks it looks like amethyst because sugilite is all purple and he thinks the temple is her evil twin sister, therefore all light purple and white. Plus I seriously doubt they’d release the temple fusion’s design in a spin-off book.
Feel free to add things to either list.