The Mirror
There are no mirrors in the Castle of the Candy Kingdom. Years have passed since Princess Bubblegum had had them removed. No one had thought to question her. The Princess is the Princess, and, as far as they know, there is still no reason to. No one remarks that the mirrors are never reinstalled, no matter how many years pass.
(Whispers are another matter, but they are careful to remain hidden. Princess Bubblegum must never be openly doubted. She is too good to the Candy People).
There is one mirror in the Castle of the Candy Kingdom. Princess Bubblegum takes it out late at night when sleep eludes her. She smiles and checks her eyes for signs of insomnia. If she isn't thorough, Jake may notice something. Peppermint Butler and Lady certainly will. They'll worry, and she can't deal with another harebrained scheme to improve her mood right now. There are Banana Guards to reinvent, a successor to create, fighting lessons to begin, and more commitments she has yet to make time for. The Lich is a burning presence in her mind, a reminder of just how precious time is.
(Princess Bubblegum doesn't think about Marceline. The vampire queen can have her illusions of Princess Bubblegum's perfection. She isn't perfect. No one knows this better than she does.)
Once she is convinced that she looks well-rested, Princess Bubblegum studies her smile. It looks real in the mirror. It feels brittle on her face. It's a crack in her skin, a mask that breaks a little more every day. She thinks she will smile the next time she cries, and the next time she cries, Princess Bubblegum knows everything will end.
(Princess Bubblegum cannot think about Finn. His smile is genuine and stabs her with each appearance. She doesn't know how much longer she can smile her lie back at him. Finn is no longer a young boy. He cannot remain her hero).
The mirror is the only one that gets to see her in her hours of distress. It watches Princess Bubblegum remodel herself again and again. It cannot judge her for failing when she is flooded. It cannot mock her as she stumbles for solutions. She doesn't have to be perfect in front of it. She tries to be anyway.
(It cannot give advice or comfort, but Princess Bubblegum chooses to ignore this. There cannot be any room for doubt).
Princess Bubblegum eventually puts the mirror away and dresses, ready to face the sunrise. Perhaps she will be kidnapped again. Perhaps Finn will bring a movie and Jake will sing. It's still hours before morning, but she has experiments to run. Tomorrow night will find her staring into the mirror again, struggling to mend the broken bits of her smile. The mirror will help her perfect it for the new day.
For as long as she needs it, there will always be one mirror in the Castle of the Candy Kingdom.
(Princess Bubblegum hates the mirror).