Upon inspection it appears to be an ordinary, slightly battered accordion with faded leather bellows and tarnished brass buttons.

Invisibility: As long as the user plays the accordion very loudly, they are under the effects of the spell Invisibility. The invisibility only works when the music is played at a volume that could wake the dead.*

Cursed Perception: The wielder of the accordion believes that the music they play is a private concert for only their ears and is compelled to play it as loud as they physically can, while every other creature in range** hears the audio twice as loud as it is played. Furthermore, the more one uses the instrument, the more they are enthralled by the sound of it.

* The statement about the volume waking the dead can be taken literally or metaphorically at the DM's discretion. If taken literally, the player cannot control the dead raised by the instrument.

** The DM has freedom to decide the range at which creatures are able to hear the accordion.

Notes: creature capable of correctly holding the instrument