How about we just simplify it to "must maintain concentration", which will have the built-in effects of distraction due to damage? Like so?
Dancing Song (Su): Once per day a verru may sing a chiming tune that causes all creatures within 30 feet to dance uncontrollably. Affected creatures must succeed on a DC X Will save or suffer the effects of an irresistible dance spell. A veeru can sing a dancing song for up to 3 rounds, and must maintain concentration. Affected victims continue dancing for 1d4+1 rounds after the veeru stops singing. Dancing song is a sonic, mind-affecting compulsion and can be neutralized by a bard's countersong ability. The save DC is Charisma-based.
Alter any of the feats and skills copied over from the pseudodragon? Maybe replace Alertness with Ability Focus (dancing song), or at least give it a +2 racial bonus?
Alignment: Always chaotic, rarely good?
I agree. Looks pretty good.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.