I think my favourite thing about Bubbline is that in the first episode that made it clear this is going to turn real gay real fast (What Was Missing), the characters still had their initial traits. Princess Bubblegum was this perfect little princess who always gets everything she wants and everyone adores her. Marceline was this “dark and mysterious” ancient vampire who’s oh so cool and nonchalant, but also a terrifying force when angered.
And now we see so much deeper into their characters. Bonnibel is actually almost as old as Marcy is and she’s been hardened into a ruthless despot, who is ultimately well-intentioned but also goddamn scary sometimes, and above all so, so deeply flawed. Marcy herself is still the lost little girl she was when she turned immortal, her blasé attitude is actually just a defense mechanism and yeah, she’s still a powerful vampire, but also a precious awkward potato most of the time.
Maybe even better than all this is the fact that they both helped each other develop. Bonnie is less tense now and focuses more on her personal relationships and sees beyond the masses of her citizens. Marceline was briefly mortal again thanks to PB and is vastly better at handling her emotions and maintaining her relationship with others.
These two are amazing.