[hider=spoil shuffle]So, we learn a little bit more about fusions, in this episode, as well as how the temple seems to be able to work. 
On the temple. It seems like any gem or any fusion that is 'keyed' into the temple has a room designed accordingly to how the gem wants it to be. 
For fusions. They are fusions, but absolutely their own person. Yes, Single Gems do have the memories of the fusions, and fusions contain the memories of the singles. They seem to be like two and two-thirds of a person mashed into one body. 
Fusions, in addition to the weapons and abilities of their single components, also have unique and amalgamated weapons and powers. Garnet and her future vision is a testament to that, as Sapphire's vision is straightforward, Garnet's reflects Ruby's spontaneity, and all of the possible branding paths one could take. 
Fusions seem to be centered to reflect on the specific high point between two gems. Garnet's theme is future, and how Rubles and Saph balance out directness and fluidity. Sardonyx seems to take in the prim and proper of both Pearl and Sapphire, while also being blunt at times, as Ruby can be. There are a number of reasons that Smoky could exist, but I think their theme is originality.

Also, isn't it interesting how, after reflecting on Jasper's corruption and fusion with the corrupted gems, we learn how Gems fuse through these high points?[/hider]