I have a few questions about Imakuni?'s Doduo and its Harmonize attack.

Are you supposed to sing one song, or may you start a mashup/medley to sing multiple songs in a row before dealing damages?
Could one improvise a song, or it must be an existing song?
Could you sing a song that cycles?
Are you allowed to finish singing during your opponent's turn?
Could you have printed lyrics with you while singing?

Is the card legal for a tournament that isn't declared on Pokémon.com? (Excluding cases of tournaments that will appear online after the tournament due to technical issues…)