She loved it ever since she was a child, when she replaced its left eye with a button from her jumper and her last piece of thread. While she was sewing the button onto him, she said, "I'm hurting you because I love you." Ash sold it to Maja to buy a new magic wand (which is a cherry blossom branch), revealing that because the doll was Marceline's favorite thing in the world, it was valuable for making potions. When Marceline found out, she furiously dumped him, shrieking "It's over, you psycho!"
In "Sky Witch," Marceline is reunited with Hambo after Princess Bubblegum managed to swap it with Maja in exchange for the shirt Marceline gave her. Maja stated that the shirt was more valuable because it had greater quantities of "sentimental freshness" and "psychic resonance," indicating that Hambo was less useful to the witch because it had been out of Marceline's possession for a longer time. However, one might assume Hambo would still have had such qualities when sold to Maja, so it is not clear why Maja had never disassembled Hambo to put any of it in her potions, as she immediately did with the shirt.
Marceline voluntarily gave up Hambo to Simon Petrikov when he briefly regained his sanity, so he could use its power as an object from the past to create a portal to go back and apologize to his former fiancee Betty Grof. Marceline said a tearful goodbye to Hambo, which created a Hambo-shaped portal that Betty used to travel to the future to save Simon.
A stuffed toy of Hambo was made available by Jazzwares as part of their Adventure Time line of plushes.
When it was first given to Marceline, as shown in the flashback in the episode "I Remember You," it was red, had two blue buttons for eyes, and a stitched smile. Two more buttons were sewn onto his butt.
In "Memory of a Memory," the toy is much dirtier and is covered with stains, patches, bandages and repair stitches. Some of its limbs have the stuffing sticking out of the toy, and only one button remained as the toy's eye. The toy is extremely faded, but there is still a red tint to Hambo, meaning that Marceline had never sucked the color from him in the many centuries of ownership.