The Axe-bass (sometimes spelled "Ax bass") is an heirloom of Marceline's family and an item in Adventure Time. It was originally a battle axe before Marceline converted it into a bass guitar, which Marceline's father calls "some kind of lute".
It makes its debut in "Henchman", where Marceline plays and sings the "Fisherman Song" for the Second Nut Son. Later, she orders Finn to kill the Dimple Plant Monster with it, but he refuses. In the episode "It Came from the Nightosphere", she plays the "Fry Song" with the bass. When Finn summons her father, Marceline's dad seems surprised that Marceline has it and takes it from her. In her efforts to reclaim it, she is shown to care somewhat more for the bass than she does for Finn, as she chooses to save it from hitting the ground rather than Finn. It shows up in "Go With Me", where she was about to play it, until Finn interrupted her by his singing outside her house. It appears again in "What Was Missing" when she plays it during the songs "I'm Just Your Problem" and "My Best Friends in the World." It's latest sighting was in the episode "Marceline's Closet," where Marceline plays it in "Journal Song".
The Ax-bass is an entirely red, double-sided battle axe with 2 chips on the right side. The head stock was most likely added by Marceline, along with the machine heads, two on each side. The pickups, also added by Marceline, appear to be single coils of unknown manufacture. The body has just two knobs (for volume and tone).
- While the bass is commonly shown to be a left-handed design, Marceline sometimes switches like in "I'm Just your Problem" when she plays picking with her right hand.
- The bass rarely ever sounds like a bass and more commonly sounds like a guitar, ukulele, and an acoustic guitar. It does, however, sounded like an actual bass in the episode "I'm Just your Problem".
- It's the most popular of three instruments she owns.
- Marceline alternates between picking, fingers, strumming, and tapping when playing this bass guitar.