An ornate chryselephantine flute, with a body of the finest lacquered mahogany, detailed with ivory and gold and inlaid with amethysts. However, to the proficient eye, it is far more than just an instrument...

If attuned with neither Flute or Blowpipe proficiency, Yon'dtara's Tongue appears to be merely a standard flute, albeit a very ornate one.
If attuned with only Flute proficiency, Yon'dtara's Tongue can be played as an action to cast any known spell of lvl 0 or 1, with no components at all. In addition, the user gains +3 to all music-based skill checks.
If attuned with only Blowpipe proficiency, Yon'dtara's Tongue can be used as a +2 Vicious Blowpipe. All attack rolls gain +2, and a nat20 causes the target to take an extra 7 piercing damage. Yon'dtara's Tongue still requires regular blowdarts to function in this form.
If attuned with both Flute and Blowpipe proficiency, Yon'dtara's Tongue gains all modifiers above, as well as the ability to spend an action to cast an enhanced magic missile called [Tooltip Not Found]. In addition, a natural 20 or 19 performance check with the Flute causes all within a 60ft radius to be charmed for 1d4 turns. This does not stack, but can be replenished by another natural 19 or 20 performance check on following turns.

Melody of Death - An enhanced spell similar to Magic Missile, Melody of Death is cast at 4th level, and has no components other than use of the flute. When cast, 5 darts of purple magical energy emerge from the fingerholes of the flute and move towards up to 5 separate targets. The spell has no maximum range, and the darts move at 60ft per turn, as long as the flute is played, taking up a bonus action on each consecutive turn, working like a concentration spell (any damage dealt causes a concentration check to maintain the spell, DC12). Each dart causes 2d8 piercing damage and 2d6 cold damage. If the darts do not hit a target before the spell is ended, they fizzle out into nothing. This spell is also available as a separate homebrew spell, for ease of access.

Notes: Requires proficiency with Flutes or Blowpipes