Wondrous item, uncommon, optional attunement
Few humanoids speak the Sylvan language of pixies and other fey, so various pixie clans have developed magic items to allow communication. Being mischievous, though, these magic items impose some slight annoyance to non-fey.
The owner of a this flute may play a short tune before another creature. If the flute has been attuned, it is a Performance skill check with a DC of 15; unattuned the DC is 20. All pixies automatically succeed. On a failure the flute owner may only communicate in flute noises (making any spells with a verbal component impossible). On a success the flute owner gains the ability to speak Sylvan. Either effect (flute / Sylvan) will last for one hour.
On a success, the flute owner may pass the flute to another creature. If that creature plays the same tune (Performance skill check DC 15) then that creature will understand and be able to speak Sylvan - speaking Sylvan to the exclusion of all other languages. The creature will still understand the other languages they speak - but all speaking will be forced to Sylvan. Spell casting with verbal components is unaffected. This effect will last for one hour. On a failure of the Performance skill check the creature will be forced to communicate only in flute noises (as above, ruining spells with verbal components) - but this negative effect lasting only for ten minutes.
The flute may be used by up to ten creatures per day (not counting the owner). It recharges at each dawn.